Ulceritive colitis blood in stool for months?

I know that ulceritive colitis has the symptoms that you have described and if it was anything like polyps, lesions or cancer the colonoscopy would have found it. I can't believe your dr has not found the reason for the bleeding nor a solution. Is all that bleeding making you fatigue? when you get your lab results back ask him if you are now anemic due to the blood loss. My cousin who is the same age as you has suffered from the same diagnosis and ends up in the ER every couple of months for the pain and bleeding and all they ever do for him is give him a steroid and send him home. It's your body and you have to take care of it, demand something be done because ultimatly you are the one having to go through this. Good Luck and hope you feel better soon.