Unfortunately, what you’re describing sounds very familiar. We get ulcers and thrush-like plaques on treatment. You can continue with the rinse, or tell your doctor; he can prescribe a prescription preparation called ‘magic mouthwash, which contains Nystatin, Maloxx, Benadryl, and Lydocaine. This is a swish and swallow medication that can be compounded by your local pharmacy, and nubs on contact, so at least you can get some relief. It’s commonly used by cancer patients, the doc should be aware of it. Pain in the butt; er… mouth, that is; but a lot of us get it.
In addition to what Bill said, some people have luck with Biotene mouthwash and toothpaste. I usually find Biotene at Walmart but I'm sure other places have it too.
At a point earlier in treatment it was if someone plucked out my tongue, put it into the microwave, cooked it halfway done then stuck it back into my mouth. It just hurt and burned like hell. There are those on this forum who have posted mixes to wash out one's mouth with but I've just tried to keep my mouth clean with mouthwash and brushing.
I had the one under the tongue at the back of throat and thought I had a sore throatuntil others appeared in one cheek area. Used Biotene mouthwash 3-4 times a day and they started to clear up.. Also had lidocaine swish by prescription to paint on before eating. Didn't 'swish' in mouth because didn't want to bite myself with a numb tongue. It takes a few days for them to start to clear.