Burning mouth, Tongue and lips

My mother is having burning sensation in mouth. Earlier Doctors treated for acidity where she took all the possible medicines for acidity out there. But at that time she had watery mouth and bitter taste. Those medicines did not help her. Now she has dry mouth and pinkish tongue which has small lacerations and fissures along the sides of the tongue but more on the left side of the tongue. She dos not eat any spices. Attimes she mentions that there is a glue type of liquid in her mouth. What one of the doctors have suggested is that the tissues in her mouth are damaged and they grow on their own, which is no medication is needed or will help. And the other one have suggested that the nerve in the mouth are probably damaged and he can give a shot in the nerve and that might help. For a while it all has been a guess work. Another one have suggested that the salivary glands are not producing saliva. So we got her the salivary artifical liquid, which she applies to her tongue and lips. And that gives her some relief. But after half an hour the burning sensation starts again. Also checked by the salivary gland specialist who stated that production of saliva is ok and also checked all the glands too which are ok. She is taking Nexium and have stopped using lyrica (nerve medicine). Nothing has helped. For the last few days the frequency of the burps have increased. Earlier she has taken Natrum phos, Nux vomica, Merc sol, and byronia. Right now she is not taking any homeopathic medicine. Please help. Than