At first guess, I would say you got an infection/cavity or problem causing nerve pain inside the pulp of the tooth. You probably need a root canal or extraction of the tooth. It may possibly be a gum problem but I tend not to see those as often.
Have a chat with your dentist and he might prescribe a pain reliever of some sort that will help you with the pain. If it is a tooth infection, you have to see your dentist asap. He will be able to examine it and might suggest to have a second check up with him if the problem persists.
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