Hi greeneyed, I can empathise with you totally - I've had this for about 8 years - not what you want to hear, I'm afraid!
A burning tongue can be due to many causes - notably a lack of B vits, and anaemia - have you had a blood test to rule out any deficiencies?
This condition is usually found in post-menopausal women, and there is a big question mark over what causes it, no-one really knows. Some evidence that it can be triggered by dental treatment ( nerve damage), and also anti-biotics (esp. Trimethoprim).
My BMS started 8 years ago - I was 57, had recently had a tooth extraction, and went to the GP when I had what seemed like a sore throat. He tried 3 different lots of antibiotics, to no avail, and I started getting a bit paranoid that it was cancer. I got a referral to the ENT, who found nothing amiss, but he did mention BMS, saying no-one knew much about it.
I did a bit of research on the web, and discovered it was EXACTLY what I seemed to be suffering from.
I found that it was almost non-existent in the morning, but escalated through the day, and worst at night. Certain things aggravated it - alcohol, coffee and nicotine were the worst culprits, and anything spicy like chilli. All typical symptoms.
Strangely enough, capsaicin is said to relieve it - a few drops of chilli sauce on the tongue, but I never tried that! Some GPs prescribe Anti depressants for it, but I never tried that either. Another remedy is Alpha Lipoic Acid, I did try that, but can't remember whether it did any good (probably not, or I would remember).
The bottom line is, that you learn to live with it, which I did, and although I still have a slightly sore tongue, it's nowhere near as bad as it used to be, and doesn't bother me now.
I'd ask your GP for a blood test to rule out any deficiencies, maybe there is something that can be corrected.
I'm sorry I can't give you more positive reassurance, and hope your problems clear up soon.