Hi there!
Well, without a clinical evaluation it would be difficult to comment specifically on the situation, though the symptoms could be related to a flare. Aut0immune conditions often tend to be related while thyroid itself could affect GI motility. It is difficult to compare a CT over a colonoscopy since both may be useful investigations. While a colonoscopy would be the gold standard for lower GI lesions it may not be preferred being invasive while CT may often be helpful. I would suggest considering a review with your gastroenterologist for an accurate diagnosis and suggestion of an appropriate management plan.
Hope this helps.
Take care!