Why do I have black stools after taking iron tablets?

Hi doctor,

I have been diagnosed with iron deficiency anemia before three months. On my latest check-up, I have seen that my iron level has reduced (5.74 g/dL to 5.72 g/dL) while my serum iron level has got higher (36 mcg/dL to 39 mcg/dL). My RBC level is normal. But my hemoglobin level got higher (11.3 g/dL) as my UBIC is still high. I made a urine test too, as I had white things in my urine for almost three months. My results say the leucocyte clusters are typical and there are 15 to 20 % epithelial cells seen. My doctor advised me to take Ciprofloxacin antibiotics. From yesterday, as I started using Iron tablets, I saw my stool in two colored like some of them are black (because of the iron), and few ones are light brown. When the stools are dropping, I have a feeling of something is hurting me. It quickly passes away, and after it has gone, my anus starts to burn. Is this a sign of bacterial infection? There was no blood in my stool.