Hi, I Noticed A Red And Painful Mark On My

Hi, I noticed a red and painful mark on my left buttocks and I thought it was a pimple and would ho away, however, it hasn't and I very painful when I sit or walk. I looked at it and saw a line where it is. It was about three inches and I've never had it until the "pimple" showed up. I want to pop the "pimple" but I'm not sure if it is one or not. The Line seems to bulge out a bit. If you know what it is please tell me hoe to heal it as it is extremely painful. Thanks