What is the cause of severe pain at the back of the tongue?

Hello doctor,

Two months ago, swellings started developing on both sides of my tongue. It was not hurting much but it used to burn sometimes and I could not eat spicy food. It is not my main issue. I do not know if there is any relevance between that and my major complaint now. So, my major complaint is that the very back of my tongue hurts very much. I consulted many doctors. They did not find anything wrong and they prescribed me antibiotics, antifungal, multivitamins, and folic acid. I took the medicines regularly but my pain was still there. Another doctor told me that it might be stress-induced. So he prescribed me a stress-calming tablet. I completed the dose and there was no result at all. My blood reports are totally normal and I am sick of this pain that I suffer from every day. Paracetamol did not affect my pain so I took Diclofenac to reduce the pain (without a prescription by any doctor) and there was a 20 % relief. But I am really confused about what to do now. I feel like the doctor cannot locate my pain by opening my mouth as it is really very inside. One ENT specialist told me to go for nasal endoscopy. But my pain is at the back of my tongue. So, will nasal endoscopy be relevant for that? I am really confused. I do not know what to do.

Please help.