Sounds like you need to have it looked at. Could be a number of things, a cyst, an infection. Can you feel it on the inside of your mouth? You could check with your primary care doctor or if it seems to be more in the mouth, you could check with your dentist. Any kind of lump should be evaluated by your doctor. If it's some sort of an infection, you may need antibiotics. Is it only painful when you press on it, or does it hurt when you talk or eat?