I had the same issue a few years ago. I think it started with shaving or an allergy to my deodorant combined with sweat. I went to the doctor because it was driving me crazy and she gave me a special lotion that I think had steroids in it that worked wonders. It wasn't an infection for me, but I have sensitive skin to begin with and I think either the razor or the shaving cream irritated me and then the scratching made it worse. Go back to the doctor and have them prescribe something else.