Please stay calm and don't freak out. Ive experienced this problem before and there is no need to be alarmed. Sometimes the uterus lining doesnt completly fall out like its supposed to from the month before when your on your period so it hardens in the body creating hard stale black tar like blood which is currently coming out. This is just the bodies way of cleansing itself and you shouldn't worry. Your period will come normally or will start now with the uterus lining coming out. Again there is no need to worry. A doctors visit is never a bad idea but i bet they'll tell you the same thing. Wait a few days and it will stop or you'll begin flowing normally.
best of luck try meditating and channeling good energy though some people may thing meditating is ridiculous its scientifically proven to relax the body and create a stronger immune system.