I'm an 18 year old fit and healthy young man, For a few months now I have been getting a horrible rash like thing on the inside of my buttcheek, it starts of red and then gets more painful and irritating, and often bleeds, it is like a burning sensation and turns into a kind off scab like thing, seems to be healed for about a week or two then returns again, this has been a constant repeat, should I be worried and go see my gp?