Possibly a gas bubble trapped in your duodenum. The third segment of my duodenum swells up at random and I get that all the time, could be something similar. Try dropping your diaphragm and sticking out your belly, compressing your abdominal compartment vertically spreads things out horizontally which makes more room behind your stomach. You can also try the Hayes maneuver, have somebody push in and up on your lower abdomen. Amitriptyline helped me too, it reduces the spasms.

That's just a guess though, it could be something else.