You need to have a good GI consultant on hand.
Some patients respond to antibiotics.
Depending what the cause of the diarrhea is, you may need different treatments. Diet with low fiber is also a good idea, and plenty of liquids. A colonoscopy may rule out inflammation within the bowel walls that may require Cytoxan or another cytotoxic drug. Consult your Rheumatologist about a GI consult and colonoscopy. These rare organisms usually respond to other family of antibiotics like Flagyl.