I got a pimple like thing near my groin, near where the thigh meets the torso. It was filled with pus and then it drained successfully. However, now there's a black aberration(skin has turned dark) where it used to be and it feels sort of hollowed out. Every few months the place gets filled with pus and needs to be drained again. Any ideas on what it is, why it's recurring and how I can stop it? Also, any suggestion how to get back normal skin tone?