I would suspect Celiac disease or dairy allergy.
You really need to see a doctor about this. Is with everything you eat? Until you can see your doctor, I'd stick with bland foods and see if it helps at all. It could be a lot of things. Is the pain on any side? Could be gallbladder. But there are no doctors on this forum; just chronic pain patients sharing. I hope you'll let us know how this turns out.