I Am Pre Diabetic. I Take 2 Metformin Pills A

I am pre diabetic. I take 2 Metformin pills a day. For a while, I have had loose stools, just enough to have to change my clothes sometimes. My doctor prescribed an antibiotic Flagyl and it helped for about a month with the loose stools. They resumed. So he has prescribed a medicine called Colestol for me to try. I have been taking this since May 30. 1 pill a day. This afternoon, when I had a bowel movement (it was soft) and afterwards, it looked as though I had poured red liquid in the toilet bowl. It was filled with bright red blood. Could this be from the new Medicine Colestol? Should I be concerned or stop taking the medication?