I finally saw my oncologist about this as well and he had no answers either, wants to wait for my first scans to see what they show, but won't treat the pain in the meantime.

I think I figured it out for myself, however. After my gabapentin ran out (no one will refill it for me), I noticed that the more nerve pain/buzzing/tingling/etc I experienced the more I tended to stick the left side of my tongue to the side of my mouth and kindof suck on it or clench my left jaw. I think those subconscious actions are causing the masseter muscle to overwork and cause pain. I got more gabapentin from a friend and after weeks of being on it steadily and weening off of my 1000mg of Tylenol and 800mg of ibuprofen every 6 hours (now down to 2 Aleve a day) I'm nearly pain free and my tongue, while not completely comfortable, is quite tolerable.

Wanted to document this for anyone else experiencing it and having useless doctors like me.