I have the same problem every month, the week before my cycle starts. I've tried eating yogurt, monistat and nothing has worked. Just burning and terrible itching for an entire week. As soon as my cycle comes the irritation leaves...my poor husband.
I went through a severe case of the same thing and tried everything including a dozen different prescription oinments, etc. But nothing worked until I asked for Diflucan pills and that did it! I don't understand why the doctors (yes, more than one) didn't just give me the Diflucan right away. I went through 4 months of burning torture. I now use Zeasorb-AF powder daily to prevent further events and haven't had a problem as long as I don't run out of the powder. Good luck.
Doesn't sound like fungus or yeast to me, especially if treatment for that didn't work.
Much more likely is irritation, from skin rubbing against skin. I suggest you try over-the-counter 1% hydrocortisone twice a day. If that fails, see a doc for a somewhat stronger preparation.
This condition may recir, but it isn't catchy. And by the way, it happens quite often in folks who aren't overweight.
Best.
Dr. Rockoff