What Causes Black And Sticky Bowel Movements While On Moxifloxacin?

I have taken Moxifloxacin for three days. Yesterday it was difficult to have a BM and when I did it was very black and sticky. Today I passed easily but it is still quite black and left residue inside the toilet bowl. My husband thinks I might have intestinal bleeding. I think it is the medication. I am returning to my Dr. Tomorrow but am concerned now.