Hi, Gayle
My husband had bad burns from scatter off his dental work - maybe that's an issue. He found the viscous lidocaine useful for drinking meals just after treatment.
Did he talk to his RO, MO or ENT about the problem? I would try talking to one of the other ones - or their nurses.
Some on this site swear by manuka honey - we never used it, but maybe worth asking about.
Is it possible that thrush as adding to the problem?
Re pain meds - my husband got off the narcotics early, but did take Ibuprohen. Maybe ask one of the doctors about non-narcotic pain relief / anti-inflamtories.

Good luck to you both!