hello and welcome to HCM forum,
i am glad you wrote in, according to the dental history provided by you it seems that you have been suffering with this problem for quite a while now, i would like to inform you that in my opinion, the pain is due to a neurological problem, the nerve
that supplies your tongue might have been affected years ago. but, the reason is unknown as your dentist
could not diagnose it.
i advise you to visit a neurologist
once as he/she might be able to provide you with a treatment plan .
Also , i assume that your tongue does not have any ulcers,
kindly be calm and see a neurologist soon,
i wish you good health,