How much blood? Blood in the stool, on the toilet paper? Bright red or darker? It would be helpful to figure out if the blood is from ulcerations or possibly just from hemmorhoids (internal and/or external).
I agree with the others that ab work shouldn't cause an onset of bleeding.
Diagnosed with ulcerative colitis spring 1999.
Maintenance dose sulfasalazine. Probiotics, l-glutamine, vitamin D and fish oil caps. George's aloe vera juice. Oregano oil antibiotic, antiviral, antifungal. Mostly grain-free and dairy-free diet. Long-term remission with only minor blips.