What causes swelling/discomfort in upper stomach area?

Lots to consider...: An ache +/- distension in the upper abdomen may originate from the stomach, duodenum, mid-colon, small bowel, liver, pancreas, bile ducts and gallbladder, spleen, abdominal muscles themselves, hernias, blood vessels that feed the organs. Sometimes the cause is inflammatory, ischemic, infectious, obstructive, or just muscle spasms. Checking with your doctor can identify what's the problem area.