Sounds to me like you have low level inflamation that's continuing. The scope might help clarify if your UC is active, but you might find it is not. I've been in clinical remission for a while and also have bad joint pain. Mine does look to be damaging my joints as well, and for some people with UC you can get other forms of arthritis other than enteric arthritis (the fun never stops with UC). As far as I can tell, GIs and rheumatologists differ a lot in their opinions as to whether achy joints is a sign of poorly controlled UC or not.
I would recommend trying tumeric and other natural anti-inflamatories. They works for some. I think they help me, although they aren't a cure.
My next option is Humira, which is depressing given I have mild colitis that's in remission.