What Specialist Doctor Would I See? This Christmas Makes Four

What specialist doctor would I see? This Christmas makes four years since I started having what looks like ulcer on my left cheek, over time it has spread to the right cheek and to both sides of my tongue. It is extremely painful sometimes I can't eat. I have been told I have Liken Plantis and Burning mouth as well as a Fungal infection. With the first two I was told it would never go away and would eventually turn to Cancer. I've seen many different doctors, done many different treatments, and taken many medicines and it still doesn't go away. How can I get this to go away and what kind of doctor can help with a definite diagnois?