There are several causes for PN actually and listed on the Mayo's site. I'm not a Dr and even if I were I wouldn't be able to tell without an exam but it does sound very much like neuropathy (nerve pain) and could even be the result of a bulging disc that's irritated by the chewing motion...or something even more trivial, just speculating really.

It is something you'll want to discuss with your Dr about and push to find answers. It may not even be cancer/treatment related, just something that should be addressed.

Good Luck

Eric