K.F.
My daughter had something similar below her lower lip. It would improve, then get worse again. We finally took her to the doctor and he stated that he thought it was a staph infection from a runny nose, etc. He prescribed bactrim ointment for like 10 days and an oral antibiotic for 5 days or something like that. It knocked it right out and hasn't been back. She had had it for like 3-4 weeks before we treated it and I would never have thought that was what it was, but it certainly solved the problem! Good luck!