I'm scared- abscess?

I have an appointment today with my GP where I'm going to talk to her about this... thing growing on my butt. (Moved a few months ago, no GI and no insurance.) It's on the line between my butt crack and the buttocks. It might be an ingrown hair, but I'm afraid it's a fistula forming. The spot is puffy, purple, and sore. Sometimes I get sharp pains if I sit wrong. I've had it for a while, sometimes it's better and sometimes it's worse. Right now is as bad as it's ever been. As far as I know I haven't been running a fever, although I could have had a low grade one and never noticed.

Am I being silly? Is this a stupid ingrown hair, or does it sound like something more serious?