If you do a search for burning mouth on this website, you might get some of the answers. I think there have been posts before.
I too have burning mouth, but mine is part of the Small Fiber Sensory Neuropathy caused by Sjogren's Syndrome.

I've heard others on the Sjogren's forum say they did get relief from their burning mouth by having their gastric symptoms treated. Please explore this problem. Have they diagnosed your gastric problems?

Also you might ask for testing for Sjogren's Syndrome.

One of the things I've found that helps mine is Biotene Gel made by Oral Balance. I use a small amount to coat my mouth. I believe they make a spray also.

Good luck,
Billye