Without examination,it is difficult to confirm a diagnosis,but from your description it looks like a mucocele. Essentially a mucocele is a condition that results from some injury or damage to the salivary (spit) gland tissue in the mouth. Rather than going into the mouth to keep it moist and to help swallow food, the injured gland releases the saliva under the surface of the skin of the mouth. This forms a bump or swelling.
Usually a mucocele goes away on its own. But if it does not, then corticosteroid injections and surgical removal by scalpel or laser are done by a dermatologist. If the mucocele is small and recent, rinse the mouth thoroughly with salt water (one tablespoon of salt per cup) four to six times a day for a few days.
My sincere advice is to get it examined from a dermatologist. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.