Stomach pain and green poop may be caused by acute gastroenteritis and indigestion. 1. Acute gastroenteritis: When inflammation occurs, the stomach may be painful and uncomfortable due to indigestion, and food will be excreted quickly. If the inflammation is caused by Pseudomonas aeruginosa, there will be green feces. 2. Dyspepsia: Due to the dysfunction of intestinal digestion, the food is expelled quickly and the stomach may have painful and uncomfortable symptoms. This results in a brief contact between the food and the intestines, which prevents the alkaline substances in the intestinal fluid from reacting with bilirubin. Also, the acidic environment in the colon oxidizes to bilirubin, resulting in green stools. It is recommended to seek medical attention and follow the doctor’s instructions for treatment of the symptoms of stomach pain and green stools.