I also have very painful mouth sores. My ENT has diagnosed it as Oral Lichen Planus. OLP can be an autoimmune disease or it can be a reaction to meds like Orencia and methotrexate. I am on oral steroids and a topical paste of steroids. It has been 10 days but not much change, especially the pain. Have a March appointment with my rheumatologist to explore the idea of a reaction medication. I am on both the drugs mentioned above plus a permanent antibiotic for previous staph in a hip joint.