It may be due to an enlarged salivary gland or lymph node. You should be examined by an ENT physician. (As an aside, I notice that you are a smoker. If you are concerned about the possibility of oral cancer, or other smoking-induced cancers, then you should strongly reconsider your smoking habit.)
Sincerely/ Robert A. Wascher, MD, FACS
www.doctorwascher.com
www.oncoguard.com