Indigestion Indigestion is pain and burning in the upper abdomen, an feeling of fullness after a meal, belching, and gas. Gastritis Gastritis is an inflammation of the stomach lining, causes stomach upset, irritation, and pain. Peptic ulcer Peptic ulcers, sores in the lining of the stomach or upper intestine, cause abdominal pain, gas, and more. Gastroenteritis Gastroenteritis is inflammation of the stomach and intestine that causes diarrhea and vomiting.