Re: oral cancer
Sounds as if you have a canker sore. I had a lot of these in my younger days.
There are medications on the market for canker sores. Try one of these, and see if the place doesn't improve in a week or so. These sores can be very painful, and if they're located where you bite them or irritate them with your teeth, they can be very sore and very persistent.
Do you have any reason for anticipating oral cancer? That is, have you dipped snuff or chewed tobacco or chain smoked for an extended period of time?
I'm no doctor. If this really worries you, see your physician.