Hey, my first response was an std but since you said unlikely... I had a boyfriend one time that had this reaction we were virgins. The doctor said it was from his laundry detergent had caused a allergic reaction: Dry skin had contributed to this. He said the area it was in is a very likely place for this to happen.. If it is that (think about anything that you have changed(soap, new clothes, condoms,) anything that might be different and try to change that.. He also recommended oatmeal baths. I might get this checked out if it doesn't clear up because it is on such a delicate part! Good Luck.