Blood in stool

Was hoping for some help, I started having blood in my stool at the end of October, after being on two courses of antibiotics, that went on for about 2 weeks, I ended up getting an abdominal CT that came back normal and got a colonoscopy that showed I had 20-25 cm of distal colitis, they took biopsies on the 29th of November and I just got the results back today, that there was no sign of anything, no colitis no crohns nothing serious, and I just had some more blood in my stool today after not having anything for a while, why is that? What could be causing the blood? I’m genuinely confused