I used bicarb. The pharmacy might have another one if become very painful. I hope you were given information from your chemo unit about this as it is standard care. Mine gave me the recipe of how much to use etc. I know our unit had other mouthwash for when got really bad. It is similar to Amosan mouth wash (which isn't made anymore) your chemist would know. It's a powder that you add to water and used following dental surgery.
Ensure your dental hygiene is scrupulous. (It may well be ....it just happens) But be gentle. Kath x.