Ron,
You are not alone. I see this in patients on occasion. If you could humor me and answer a few questions I may be able to help you.
Do you wear dentures?
Have you had back teeth extracted recently?
Did your radiation fields include the corners of your mouth?
When did this situation first occur?
How long has it persisted?
If you can answer these questions I may be able to offer some assistance to you.
Cheers,
Mike