First understand that no one over the web is going to be able to tell you exactly what is wrong. So having said that, let me say that there are plenty of benign things that this might be rather than the big "C". Anytime you have something that does not heal with or without treatment in two weeks, it needs to be looked at more seriously. While your dentist is a good starting place, if he doesn't come up with a definitive idea what it is and it has persisted for over 14 days, you might consider an oral surgeon, or periodontist both who are familiar with looking at soft tissue abnormalities in the mouth. If either thought it was something suspicious, they might take a biopsy, which is quick and painless, to see exactly what's what at a microscopic level. You don