Hello! I have been through your question. Related your concern I think this is not arthritis. You should know that CellCept (mycophenolate mofetil) is an immunosuppressant, a medicine that lowers your body s immune system.Auto immune hepatitis is disease that should treat with immunosupresante drugs. Like all drugs this could have a lot side effects that includes lower back or side pain,unusual tiredness or weakness ,muscle pain (myalgia), weakness in the skeletal muscles (myasthenia), pain, paresthesia, back pain ect that explain your symptoms. In your case you must not stop this medication but you must talk with your doctor to tell him related this symptoms. I hope my answer help you. I wish you a quick recovery.