I am a 5-10, 175 lb,32 year old male in good health. I am a military pilot with frequent physical and medical examinations. About 4 days ago, I got a pain in my upper abdomen that I can only feel when I am up walking around. When I sit down, or when I lay down the pain subsides. It feels like a side ache, due to running or walking after a carbinated beverage, but it usually occures after about 25-50 steps.