It's hard to identify from the pics provided but it seems you have a mild condition which will improve on its own. Meanwhile it is strongly advised to immediately stop habits like smoking alcohol tobacco chewing or any other kind of debilitating habit that you may have. Secondly try your best to maintain a good oral hygiene by brushing twice daily and using a non alcoholic mouthwash. Thirdly if you feel any sharp edges present on any teeth on the affected side they may be causing any form of cheek bite or injury, do get them blunted immediately by your doctor. Mild conditions like these resolve on their own but takes quite some time. Also, in order to confirm the findings you have an option if taking a second opinion as well.