Anthony, I am so sorry this is happening. What you describe might be several things. I hope that you can avoid being diagnosed with RA but in case you are and even if not, welcome to our community. You may not know it but we do not provide medical advice or make suggestions about what to expect.
We always refer people to their doctors. There is a good reason for that. We are not doctors, and we do not have medical training. even if we did, giving direct medical advice would be inappropriate since we have not seen your records, or examined you in person.
All of that being said. I can say I did not have mouth sores until after I started using Methotrexate. My issue was that Methotrexate was reducing my immune levels and allowing infection to take hold. My Rheumatologist suggest increased Folic Acid to reduce the sores. He suggested an over-the-counter folic acid supplement. The pharmacist helped me select one.