Help my guinea pig is self mutilating!!!!?

Hi my guinea pig stewie has been self mutilating his area close to his butt for the past 5 days. I took him to the vet and they cleaned out the area around his penis. The substance that they took out was waxy and hard. I bought him home and he seemed that night to be healing but then the next day he started doing the same thing again. He is also on metacam and enrofloxacin and animex for the wound. I need some help because going to the vet has already cost me $500 plus and I dont want him to be in pain anymore.