Reflux only when sitting?

So after multiple er visits, a 14 day holter monitor, stress test, etc … I’ve ruled out cardiac symptoms. I then went on famotadine and a PPI, followed by a colonoscopy and upper endoscopy that have found nothing remarkable.

I can’t sit in an office setting, or drive my car, or relax at home… without getting center chest pain that radiates to other areas of my chest, sometimes with belching… it feels all around uncomfortable and awareness of the feeling makes it a rather distracting experience.

Any advice on what to do next? Who do I see for further tests and what tests or medication might be worth trying?