My response may be long, only because I'm experiencing the same thing as you. I seem to be really tired at 11a, 3p, 8p and sometimes 5p. I talked to a friend who is a nurse practioner and she explained that my 11a/3p was probably my breakfast/lunch wearing off. That my body was going into crash mode,so I should eat more protein. I told her I was scheduled to see an endocrinologist (endo) April 6. She said that they do most of the test in the office and asked if I'd see my primary physician. I decided to go to my primary doctor first, because I could get in the next day. He gave me a b12 shot, which seemed to help for a few days. All my results came back normal. They also tested my thyroid and it came back normal. I thought it was my thyroid because I'd had the left nodule removed about 15 years ago and I am not on any medication. I started getting tired after nursing my now 6 year old and felt it was due to the hormones. But I get so tired that I have to lay down, when at home, of course I can't lay down at work. A friend at work mentioned that she was so tired that she went to an endo and he prescribed a heavy dose of vitamin D (the one you take once a week) and some type of cream that she has to rub on. She says it helps tremendously. So I got the endo's name and number. I've even tried two different products that supposedly help you with energy and neither has given me any relief. I will probably cancel the endo appointment and go to one that my friend referred me to in Irving. I did start taking some prenatal vitamins and back on my probiotics. I'm hoping those will help, but I can't go on like this. It is not normal. Of course the other thing is I do stay up too late (11p - 1am), so I'm working on going to bed earlier. If I don't see some progress with both the vitamins and getting more sleep, then I'll reschedule the endo appointment. I get so tired sometimes that I can't do regular household chores. By all accounts I'm 5'5 and 131 lbs and fine with the exception of being extremely tired. Please PM me if you find some results that help. Advice to me, was to start logging the times you feel tired and what you eat each day.
p.s. I did tell my ob/gyn last year about being tired and she recommended I get some exercise. However, I'm too tired to exercise and you will probably be able to relate to that answer. I'll pray for us both.