Hello, Yesterday I Went To The Doctor And Received Bactrim

Hello, yesterday I went to the doctor and received bactrim for a uti. I took one pill. An hour or two later I started having severe cramps. So bad that I was nauseated and crying. I went to the bathroom a few times and then realized I was bleeding from my rectum. Like diarrhea but just straight watery blood. No fecal matter. I called my doctor and they gave me cipro. They said I should be fine after I take that. Well that was at 11 am and it's now 7:30 and I still have severe cramps, I've passed some blood clots but I havent passes anything else.