I get stomatitis once a month, it lasts 10-14 days and then I go a cou…

I get stomatitis once a month, it lasts 10-14 days and then I go a couple of days without stomatitis, and then a new one pops up. I think it's because of weakened immunity and cavities. ? Help me please, what effective medications are there? Maybe there is a blood test that checks for stomatitis? I'm so tired of stomatitis ((( I can't even eat or talk, today I even coughed through hellish pain)