I had a tooth extracted about 18 months ago. About 4 weeks ago I noticed a very sore tender spot under my jaw (where the tooth was extracted) when I accidently touched it - other than that I would not have known there was a problem. The pain only occurs when I touch the spot, and there is a very slight swelling as well. I have no pain other than that and can open and close my mouth without difficulty. What could this be?