Started Having Stomach Problems Thursday Evening .About Every Thirty Min.I

Started having stomach problems Thursday evening .About every thirty min.I felt like i had to use the bathroom but then each time I hurt really bad from my waist down and would only pass blood.This continued thru.the night every couple of hours then Friday morning I went to the urgent care and was prescribed medicine that has stopped the bleeding but now it appears to be ,maybe tissue in small amounts that I pass.I no longer have pain but I would like to know what could be causing these symptoms. No thank you I thought this was a service offered thru.Dr.Rusynyk and since I have to make a appt. anyway.No since in paying twice.