Medical question, please help!?

a month or two ago, i noticed a sac under my skin, in between my leg and scrotum. it was pretty big, and sometimes felt like a bruise. when i woke up this morning, there was pus or something coming out of a big hole that wasn't there before. now only blood is coming out, but i think there might be pus in the blood because the blood is very light colored. But the sac isn't getting smaller, although the area around the hole seems to be turning darker. the hole looks black. what is this?? how do i get rid of it???