How discouraging when the doctors are not even sure of what's going on!
It sounds somewhat like heat rash. Sounds silly in the colder weather but when you begin sweating and your clothes rub on your skin a rash can develop. More so in the hot months.
I really am just guessing here, sorry. I always tell my family, when they have heat rash, raw skin, etc. to try the medicated Gold Bond powder. (That and pepto is all I need!) May help with the itching and help cool your skin.
Dollar General has their own brand of the powder and it's only a $1! Really have nothing to lose since you've tried everything else it sounds like.
Good luck to you.