I'm not a doctor and I don't play one on TV, but I do work with a bunch of gastroenterologists

The upper GI equivalent of IBS is called "functional dyspepsia". But I don't think it'd be accurate to diagnose you with anything right now considering the only test you had was a US.

It's up to you how much digging around you want to do to figure this out. As others have said, the GI system is fickle and sneaky. The recommendations for celiac and lactose testing are good. You can either go in and have them done, or experiment at home by cutting dairy or taking Lactaid or something similar. Though the typical symptoms of lactose intolerance are crampy abdominal pain, bloating, and diarrhea. But as I've learned over the years nothing with GI is typical in everyone

Other tests you could consider are an upper endoscopy to ensure there's nothing going on with your stomach or first bit of your small intestines. Not a fun procedure, but it'll tell you if there's something in there causing your symptoms.

My recommendation would be to see a gastroenterologist if you haven't already. One that specializes in upper GI symptoms. Believe me, all GI's are NOT the same. If you live in a big city, then a major hospital would have more docs for you to pick from. Ask them when you make the appt.

Good luck and I hope you can find some answers.