it is very likely a gluteal abscess or perianal abscess, but could be a fistula also. no sure way of knowing, unless u see ur stool coming out with pus and blood as well, which is rarely the case.

abscess tends to be recurrent, and quite often in the same or similar spot. some people are more predisposed to develop abscess, E.g. diabetic, poor hygiene, overweight.

You need to see a surgeon, and remove the whole thing. Sometimes an abscess can break and heal by itself, but the residual pocket is vulnerable to develop an abscess again in the future.