I Have A Sloughing On The Inside Of My Mouth

I have a sloughing on the inside of my mouth around the edges of my lips and cheeks. part of my tongue feels like it has been slightly seered by something hot only just lightly, not all the time, and not the whole tongue. Although it never goes away it does get better and then flare up. It does not itch and has no pain or stinging. I have had a biopsy and tried meds for thrush. any answers. Dr just looked at it and had no idea