Peptic or gastric ulcers
These ulcers are sores that appear on the lining of the stomach. This sore can cause bleeding and turn the color of your stool black. These sores often develop after the mucus layer of the stomach has been compromised by flank one.
Peptic or gastric ulcers [5] are typically painful, and the pain and bleeding often increase when and after eating. Most are caused by infection with the Helicobacter pylori bacteria, but they may also be caused by chronic use of nonsteroidal anti-inflammatory drugs (NSAIDs). Signs that you have a peptic ulcer include abdominal pain, feeling full, and black stool.