I'm at the end of my period and have also been drinking a lot of red wine, i'm having diarrhea which is black and slimy?

Black stool: If your diarrheal stool is not mixed with your menstrual blood and you are indeed passing black stools, a serious cause could be bleeding from high in the gastrointestinal tract(esophagus, stomach or duodenum). Other causes of black stool are taking iron supplements or peptobismol. If you have any weakness or concerns about gi bleeding, go to the hospital emergency room for prompt care.