Why is my stool black? I've been taking biotin, iron, epa-dha complex and multi-vitamin pills. My hair has been falling off more than usual as well.

Agree with Dr. F. The things you are taking are neither helping nor causing hair loss. You may wish to stop taking iron and see what happens.
Get HPV vaccine.
Hello. . Hello. I can't diagnose the reason for you black stool. Iron supplmentation can cause bowel movements to turn black. If you have black bowel movements that are sticky and malodorous, this can be consistent with gastrointestinal bleeding. In that case, it is very important that you not delay being medically evaluated. Take care.