Hi A., I know this is a really long response, and maybe you've already read it, but I've added some more thoughts and would encourage you to read it again! Thank you so much for reaching out to Mamasource!
I really understand how sad you feel. My miscarriage (after 5 years of trying for a third child, at the age of 40) was the saddest thing I have ever gone through in my life. I would encourage you to grieve fully, create a meaningful ceremony to celebrate this being's short life, and talk about your feelings with people who will understand (many people don't understand how painful miscarriage can be). I think it's important to take some time to grieve before planning to conceive again, also time to allow your body to heal. You can trust yourself to know when it is time - it may be right away, or in a few months.
Miscarriage is very very common (I have heard figures as high as 85% of pregnancies end in miscarriage, many of them before the mother is aware of the pregnancy). It is not your fault, it's nature's way of ensuring that healthy babies are born, by allowing those who are not healthy to pass on. There are also many spiritual ways of looking at miscarriage - such as that the soul only needed to come into physical form for a short time to fulfill its mission; and/or that this being came to you for this short time in order to help you grow in some way. Maybe this same soul will come back to you again, or maybe this time was all that was needed, and a different soul will come next time. You could create some quiet time and have a dialogue with this being, appreciating the short time you had together and expressing your love and maybe gaining some understanding of the meaning of this.
I would encourage you to really appreciate the extra time that you will now have with your son and husband, before adding a fourth person to the family, and that you welcome all of your feelings and your husband's as well (in addition to sadness, you may experience anger, fear, relief, guilt, etc). Your husband may have similar feelings to yours, or may be quite different, and it's important to acknowledge that. And although your son may seem too young to understand, I think it's really important to include him in your process, realizing that he can at least sense that you are sad and probably wonders if he did something wrong (as is natural for young children to do). You could offer him a simple explanation, I'm feeling really sad right now and it's not about you, I love you very very much and am so glad you're here. (or you could give a more detailed but still simple explanation if it seems like a good idea - like, I really wanted another baby to come, but the baby isn't going to come right now, and I'm really glad you're here). Really paying attention to how he responds as you talk with him, and empathizing with his feelings too. He may have had a connection with this being and may be feeling the loss himself, so I'd just be aware of possibilities like that and be extra attentive to him and use your intuition about what to say to him. And if it is sometimes hard for you to be present with him because you are having feelings, please find ways to give him special care and get good support for yourself.
Also, and this is not meant to diminish in any way your sadness, but it may be better for your son that his sibling will be born when he is a little older (some people consider that 2-1/2- to 3-year spacings between children are optimal). I realize that at the age of 35 you are probably concerned about your biological clock, but, unless you have other health problems (and it sounds like you don't), it is highly likely that you will be able to conceive again, although there are certainly no guarantees (I wasn't able to have another child after my miscarriage, and it took a while to really come to peace with that - but now I have three wonderful grandchildren!). And, again, this is not to try to diminish your pain but to offer another perspective, there is much to be said, in these times, for having only one child, to whom you can more fully devote yourself and who can grow up feeling perhaps even more loved and cared for and therefore more able to love (and there is also the serious issue of planetary overpopulation). Of course children need to socialize with other children, but that can happen in many other ways besides having siblings.
As far as going to see a doctor, I would say there is no need for you to do that (especially since it sounds like you'd rather not), as long as the bleeding stops and you have no signs of infection or anything. You can trust your body to clean itself and prepare itself for conception again when you are ready. I'm sure there are herbs that can specifically help with this, that you can find out about. Otherwise, I'd encourage you to really focus on taking good care of yourself, get lots of good exercise as it feels right to you, eat really well, and do whatever you can to cleanse and prepare your vessel, your temple, to welcome a new being when the time is right. I'm sure there are some books and internet sites that could be very helpful for you as well, but even more important I think is to trust yourself and really appreciate the family you have.
I've just read the other responses and really agree with Janet H, Andrea H, Theresa S, and I really think the best thing for you will be for you to tune into yourself and trust yourself to know whether you need to consult with anyone else. If you do have any signs of problems or just want to check with someone, I'd call a midwife rather than a doctor. I agree that D&Cs are usually not necessary, are very invasive, and can be quite traumatic, and doctors are probably motivated by fear of lawsuits rather than your wellbeing. I feel sad that so many women turn so much power over to doctors. I'd encourage you to empower yourself by accessing information by internet or books, and especially to take this opportunity to really tune into your body and further develop your own bodyknowing (which will help you greatly in your next birthing). (one issue though you might want to consider - if you have Rh negative blood type, it might be good to find out if a Rhogam shot might be a good idea. I don't know what the current thinking is on this, but when I miscarried 20 years ago I did go in for a shot, at the midwife's recommendation).
With both of my births, even though the second one was at home, I experienced way too much intervention and intrusion into the natural process, and in a way my miscarriage actually helped me to heal from those traumas because I went through it at home, in my own way, in my own time, with only people around me whom I really wanted to see. (it did, by the way, hurt quite a bit for a while, the cramping). I was actually going through a difficult divorce at the time and so had no husband to turn to for support, and for me it was really important in the first days to have supportive friends come over, just to be there with me, as I didn't want to be alone. I named the baby and had a ceremony, planting a rosebush over the tissue. You may also want to have some peaceful time where you can be alone for a while (ask someone else to take your son somewhere fun), maybe spend time in nature, maybe do some journaling or artwork or dancing or singing. Maybe find a good therapist or counselor to help you through this (especially if it seems like this miscarriage is bringing up feelings from something in the past - this could be a really good time to work through some other things). Also, if you have any unresolved feelings about how your first birth went, this could be a really good time to work through them before getting pregnant again. Also a good time to learn more about pregnancy and birthing (I'm a strong advocate of homebirth, and especially waterbirth, allowing the natural process to unfold without intervention, with a supportive knowledgeable midwife holding space and encouraging the unfolding, only intervening if necessary). If you do want to consult with someone about the miscarriage, this could be a good time to call different midwives, to find someone you resonate with, to check you out and help you through this time, and to begin to develop a relationship tha you would continue after you conceive. Wishing you the very best and sending you love and light!