The Washington Post has a series of articles called medical mysteries . One is titled burning tongue and made me think of the person here with a burning mouth. Also today i discovered I have low ferritin levels and need to take iron supplement even though CBC said my iron was normal, Ferritin measure stored iron . Low levels can be the result of a number of problems but low levels will cause disturbed sleep, hair loss, fatigue and burning tongue/mouth.
I don't want to play doctor just thought it might be interesting to read the story on the Post. Also several of the stories are about people who refused to accept their original diagnosis and kept going to new doctors till they found the answer. One is about a doctor with a rather simple problem who had seen five specialist till reluctantly he went to his 4th dermatologist who diagnosed him in 2 minutes. He had retired because of the problem which was easily resolved.
so don't give up , don't settle for a idiopathic diagnosis.