Welcome to NeuroTalk:

There are two possible things to try for your problem.
Then you really should come to our Peripheral Neuropathy forum for further ideas.

http://neurotalk.psychcentral.com/forum20.html

1) Have you had your B12 tested? You should be at least 400 US units... labs in US are still reporting low levels as "normal" so they don't flag these for the doctor...Therefore get your numbers! Don't accept "normal" . We have a complete thread on PN at the top of the page -- all about B12. Many people in US today are low in this and are not being caught by doctors accurately.

2) Lipoic acid has been used in burning mouth. We discuss this useful supplement on our PN forum often.

Also you may be intolerant of some foods you are eating.
1) gluten is the main culprit. Going gluten free may help.
2) other foods can cause this too. Nightshade veggies and peppers can cause all sorts of burning sensations in those sensitive to them.

Also impaired glucose tolerance is a possibility and precedes actual diabetes. Cutting out sugar and refined carbs, and eating more veggies and lean protein may help.

Also...an ingredient in mouthwashes and toothpastes, may be causing this. It is called triclosan, and there are recent reports on it concerning it causing nerve damage and other toxicities.
Find a new toothpaste without it. an example is Colgate Total, but many many other brands have now added this chemical.
It can be very irritating to some people.

Stop using mints/ sugarless gum, etc for a while and see if that helps.