I think it's wise to get Lupus ruled out. That seems to fit your symptoms very well. If the softer tissue is affected too fibromyalgia is very similar to lupus, but the diagnosis for that like IBS is often exclusion of other diagnosis.
Both are just inflamation of parts of the body. In your case it may have affected the bowel first and they diagnosed that as UC? Did you have a pouch due to dysplasia?