Welcome to the forum. Sorry you're struggling with fatigue and joint pains though.
Those are common extra-intestinal manifestations of UC. Those can linger into a remission some tines. Sometimes fatigue is rooted in an underlying anemia or vitamin b12 deficiency, make sure those are ruled out (if not already). There's a slight chance of remicade-induced lupus but that's pretty rare.
A couple videos from the Michigan IBD school on this:
Fatigue in IBD part 1https://youtu.be/xa_njg1aubk
Fatigue in IBD part 2https://youtu.be/bbs7m9ohtzo