The below paragraph I copied form the Merck Manual, it all holds true for me.
I knew I was allergic to Propylene Glycol long before I had BMS.
Watch your toothpaste because alot of them have the above ingredient in it.

Merck Manual -
A common cause is the use of antibiotics, which alters the balance of bacteria in the mouth, leading to an overgrowth of the fungus Candida (a condition called thrush). Ill-fitting dentures and allergies to dental materials may be causes as well. Overuse of mouth rinses and sprays may lead to burning tongue syndrome, as can anything that leads to a dry mouth, such as alcohol or tobacco use, and many medications. Sensitivities to certain foods and food additives, particularly sorbic acid and benzoic acid (which are food preservatives), propylene glycol (found as a moisturizing agent in foods, drugs, and cosmetics), chicle (found in some chewing gums), and cinnamon, may play some role. Deficiencies of vitamins, including B12, folic acid, and B-complex, can cause burning mouth syndrome. Iron deficiency has also been implicated.

I know it is the most painful(my neurogolist told me this burning sensation is a form of pain)that I have ever experienced, I thought I was nutty until I actually found a doctor that could tell me my symptons before I could tell them to her. That was a wonderful feeling. I had one to many doctors to look at me as if it was all in my head. But its not it is real, so hang in there, you can handle it. You are really stronger thant what you think you are.
All of us have our moments, just say some prayers and try not to think of it.
God bless.