When I had mouth sores (during chemo), following worked (different things, different times):
1. Pretreat sores with Kanka (over the counter, drugstore), contains an anesthetic, pretreat shortly before eating. Hurts when applied, then feels better.
2. A pink mouthwash concoction the nurse wrote for, containing lidocaine and an antifungal, goes under various names--such as magic mouthwash.
3. Rinse mouth with baking soda solution.
4. Believe it or not, pool water. Sores would feel better after I had been to the pool (chlorine). They were visibly less inflamed/red.
5. There are some reports (unconfirmed) that some have had the sores successfully treated with a laser by a dentist. The literature suggests that actual mechanism (cause) of the sores is unknown. Any treatment is lessening symptoms, not curing cause.
Also, my mouth sores seemed to come/go in cycles. If I tolerated it, they eventually peaked and then got better.
Hope this helps. Best wishes.
Bob