There is an IBS board here. People with IBS have some of the same symptoms, but not all of the same. I think it's often discomfort and frequency, or the other direction with nausea, bloating and constipation.
Bleeding, tenesmus, urgency, mucus, accidents, D - these are UC symptoms. UCers can also have fevers joint problems, other AI illnesses, severe pain...
I think the only way to know if it's IBS would be to get a scope, have it be clear of inflammation, and still be struggling with symptoms. If you're having symptoms and you have UC, I'd imagine the majority of the time, it's due to inflammation, and a scope would be able to show that.
I don't know much about
IBS. Like I said, I was told I have it, but it was always UC for me. Check out the iBS board, you may find some answers.