My wife is having a problem..?

Ok so me and my wife have a child together, and no were STD's involved on either half of our sex lives that we had before us so do not even try posting that as a usable answer. Ever since about 3 months into her pregnancy she has had the issue of a yellowish discharge from her vagina and the only explanation for this discharge is that she has excess estrogen. This discharge causes her burning and itching to the point that she could and sometimes does scratch herself raw. We have also taken in the consideration that it might have been a yeast infection seeing as how similar the traits are. Almost two years after her pregnancy she has been to about 3 different doctors and all of them have blamed it on either her birth control, a yeast infection, or the newly used excuse of too much estrogen. This problem is ruining our sex life and because most of our relationship was purely physical in the beginning, and as we all know you can't chop off the base of a tree and expect it to stand up after that. So on top of it ruining our sex life, it causes us momentary anger all because of this stupid, probably easily fixed issue that the doctors aren't considering. We have tried switching from one birth control to another birth control. We have also tried just condoms. We have tried using Vajisil, which only seems to work for the itching, and we have tried any yeast infection medication. Could their possibly be something that we are overlooking or perhaps an issue that both of the doctor aren't covering. I would appreciate any positive feedback. Thank you.