It sounds like an ulcer. I get them usually right before I get sick. The good news is that they aren't anything serious and they will go away on their own. The bad news is that they usually last for about a week and can sometimes (depending on size and location) be really painful. What I have found works the best is before you brush your teeth or eat, put ambesol or camphophenique on it. They can be found at any drug store and while they taste nasty, they will numb the area so you can brush your teeth or eat without being in a lot of pain. I have found that the first couple of days when the ulcer is just starting its just kind of annoying more than anything else. Then there is usually 2-3 days when it is really painful and then after that a couple of days when it is annoying before it finally goes away on its own. Usually lasts about a week. Hope it starts going away soon - its nothing serious but just tends to be annoying. Good luck!