You should return to your doctor as soon as possible and have them check this further!!!
Black stool (that is not the result of any type of Colon Cleanse resulting in mucoid plaque)...partcularly if it occurs following pain...can indicate that you are bleeding internally. Blood that is coming from the upper GI tract...such as the stomach or upper part of the small intestines...will appear black as a result of traveling through the digestive juices, and will often appear powdery or like coffee-grounds.