Will, welcome. this sounds so much like my husband's diagnosis. He just finished #35 of his radiation treatments today. 3 chemo treatments every 3 weeks.
I have to say he has said his pain has only been a 3 or 4 throughout the whole process. His biggest complaint has been the feeding tube hurting and having issues not so much his mouth. He just started pain medication on week 6 of treatment. But everyone is different.
My husband took disability from the day he got the PEG tube until 2 weeks from now but i"m going to petition for a longer disability as his mental acuity is pretty bad right now and he has a desk job in IT.
Hang around here and read some of the posts. I'm a caregiver but it's been a lifeline for me.