A bump on your gums next to a tooth can be an infection draining out. This is called a parulis. Your dentist will check the teeth nearby this lump to see if any of them are infected and will take xrays to check. A root canal will fix this.
If it is painful then it could be a pocket of infection, or an abcess tooth. It could also be a pertruding tooth. Either way you should see your denist about it. A lump on your lower gums is not normal and needs to be checked out by a professional.