Hi, have you tried doing a CT scan that includes both the chest and abdomen? Sometimes pain in the upper right abdomen can even be something from the lower lungs that feels like it's in the stomach. What about blood tests? Is there anything in the blood tests? I would suggest trying to continue to perform comprehensive tests to understand what the problem is.

I get some pretty intense intermittent pain over one of my kidneys and i found out it was actually spasms in the muscle attachments around my ribcage. The only thing that ive found has really helped is muscle relaxers when its really bad and stretching. Muscle spasms with AS seem to be pretty common from what ive been told by my doctor