Hi, B.! I really feel for you. I, too, have a history of depression and I know pregnancy and small kids can make it really hard to cope. I am so glad you were able to reach out for help on this board!
The first thing I can tell you, from experience, is that you must tell your husband. If you want to say something like, "I have something to tell you. I'm worried you're goign to get upset but I really need you to support me", then please do, but you must tell him. This is one of those times when you need to lean on his support for a bit so that the whole family can stay healthy.
I hope he will support you in reaching out some more. I think one of you should probably call the psychiatrist's office and ask why this happened. Personally, I'd rather pay the fee than switch doctors, but I don't know your situation. If they seem sure about this, ask them for a recommendation to a new psychiatrist. Call your ob's office and ask for a recommendation (also tell them what happened--they may want to keep this in mind before they recommend the psychiatrist again).
I don't want you to feel overwhelmed, but you also might want to ask your ob to keep an eye on your thyroid levels (TSH) during the pregnancy and after. Thyroid and PPD are strongly linked, and I personally feel like my thyroid and depression problems are all linked.
Do not stop your meds on your own--especially when you're pregnant!
Give yourself a break each day. Take fifteen minutes to just sit on the floor and play with your girls. That helped me a lot. So did getting a notebook and, before I went to bed each night, writing down one amazing or cute thing my daughter did or said. No matter how awful the day seemed, there was always at least one thing.
Those two things really kept me going.
I hope that everything works out for you. Tell your husband, and I'm sure you can work it out! Always remember that this is a disease and not something you did or chose.