Suggest Treatment For The Rash In Butt Crack

Hi, I am female this started when I was around 15...I am 25 now. I have a rash all the way up and down my butt crack. It is very itchy; the rash is slightly dry and flaky. When I stratch, I notice flakes of skin falling. Recently, I have noticed that it has spread to my pubic area. It is not itchy there, but when I go to the bathroom, I notice peels of skin ont he toilet paper every time I wipe; it is on the outter and inner sides of the labia majora...nowhere beyond that point. It all started when I began to wear lace underwear. Everytime I would wear it, I'd have a flare up that would go away eventually. However, now it has not gone away despite no longer wearing the lace underwear. What could it be?