In major issues like Colon Cancer, black tar colored stool is due to melena, and this is usually found in
ascending colon(The right side of your abdomen) So opposite side of where your pain complaints are.
Black colored stools can be caused by many issues, not just diseases. It can be caused by food, high iron, medicines,etc. But to be on the safe side, and to avoid causing more issues or prolonging it, you will want to visit your doctor and let them know whats going on.