thanx for sharing your concern,
the symptoms you are presenting here may be because of chronic cheek biting
reasons for this may be several like
1. improper occlusion.
2. space deficiency due to wisdom teeth.
3. ulceration at the exit of the salivary duct that opens at the cheek.
4. any causative traumatising agent.
so i will advise you to visit your dentist
& go for a proper clinical check up.
meanwhile use a topical gel like dento or dologel 4-5 times a day, it will be fine.
hope this helps.