You should definitely get a scope, and another opinion. I changed GI's about
2 years ago because I kept having similar sypmtoms, had a colonoscopy with the new GI and was in remission at the time. I think it was the IBS, not the UC, but wanted to really find out what caused those symptoms and what I could do. My colonoscopy showed as though my colon was almost normal and my blood tests negative. So this 'new' GI (who was a resident) told me to stop all my maintenance meds and told me I did not have UC. And now two years later I am still trying to get over my first real flare in 10 years.
I had a feeling I should get another opinion when he told me that but I didn't. I wish I would have as I'm sure I wouldn't be in this situation if I had trusted my inutuition that something was not right with him. I don't go to him anymore, by the way.
You can have a flare up without bleeding, but what I've found is its either usually IBS or my UC getting a little 'active'. Meds always settled it down for me though. Prilosec seems to take away my colon rumbles (something I discovered completely on my own but my new GI agrees with).