For The Past 2 Months, The Inside Of My Mouth

For the past 2 months, the inside of my mouth on the left side only is puffy and my mouth is very dry. There is no pain and the right side is fine. My dentist agrees it's puffy but took X-rays and there seems to be nothing wrong that he can see. He also looked inside my mouth with a strange light that is supposed to show cancer as bright white spots, but he saw nothing. i'm takin no new medications and haven't changed my diet. Any thoughts?