I have bad stomach pains when my upper body is vertical.?

I felt fine laying in my bed, when I stood up I had severe pain. Sittin in my computer chair I have to slouch forward in order to not feel the pain as bad. When standing up the pain is really bad, I can only stand for about a minute or so before I have to squat down and aleviate the pain. Obviously the first sign is gravity causing some tention somewhere. I have a fairly strict diet, I run 6-12 times a week and weight train 4 days a week, work in a warehouse. I have no issues with going to the bathroom, nor acid reflux.