Hello, Black stool that is tarry in texture and foul smelling is often a symptom of upper gastrointestinal bleeding from the esophagus, stomach or small intestine. This is called melena. Rectal bleeding of bright red blood with clots, sometimes mixed with stool, is called hematochezia. (note - taking iron supplements orally for anemia could cause black coloured stools). Most common cause is peptic ulcer,, they are other causes too, these bleeding in GI tract causes loss of blood and make you anemic and feel weak and tired. Please see,, gastroenterologist or general surgeon to search for cause by some procedures like endoscopy, colonoscopy few more as needed.

Please get these things done...upper GI endoscopy... Colonoscopy.. And a CT scan of abdomen...get these done sir and get back