I had the same problem a couple of years ago. I went and saw my ENT (Ears, Nose, Throat) doctor and they insisted they pop it. It hurt like hell, but went away. 3 months later it was back! While I was getting my teeth cleaned by my dentist he saw the bump and replied, "Oh, you have a tooth that has died and you need a root canal." Sure enough, the white, puss filled bump was caused by the dead tooth disengaging from the root.
See your dentist and don't let any ENT doactors talk you into slicing and dicing before you have X-Rays done.