"diagnosed with psychosomatic pain relating to" your stomach? Isn't all pain that way, really? I mean, it's all a matter of the nerves telling your brain and your brain decides it's pain...
Stress. It sure could be stress. Muscle spasms from over (or under) use, or tightening due to stress.
Ok, I'm really irked by their dxing "psychosomatic pain."

SOMETHING is causing the pain. I mean, even if it's stress, it's still something. We are so intertwined, mind/body/spirit that there is no dividing us up to "body" or "mind" or "spirit" you know?
However, I do hope they checked your appendix, and did an EKG since they were doing the other weird tests.
TC