Period changes can cause constipation or also diarrhea during different times. Initially usually diarrhea due to high progesterone levels and this can decrease the following days and then cause constipation. Maybe you're constipated at this time and that could be why your bleeding from there. Also there is this thing most people don't know, during your period your anal canal can get tighter and stiffer due to the hormones causing contraction going over there. That could cause bleeding if it isn't accompanied by diarrhea (Basically tighter anus + thick poop can cause the bleeding). Don't worry, once it heals it will stop bleeding maybe to kind of help that process, lean more to liquids than solid foods. Don't be traumatized, our physiology heals fast! 😉