We can often have a disconnect between synptoms and actual UC inflammation. Happened to me before.
We can get joint aches as an extra-intestinal manifestation of UC. Sometimes it's related to the amount of active inflammation we have: aches worse during flares and goes away during remission. Other times the aches are a constant regardless of how well our UC is doing. Sometimes it's a second immune condition like rheumatoid arthritis.
Here's a link from the ccfa about
Moderator Ulcerative Colitis
John, 39, UC Proctosigmoiditis
Rx: Remicade @5mgs/kg/6wks; daily 75mgs 6MP, 4.8g generic-Lialda, and rowasaSevere flares make the common toilet worse than any medieval torture imaginable. The rack? Bah! I survived the thousand razor blade poop for weeks!