I can, and do, very much relate to your experience with this SOB situation. Mt personal journey with my SOB began three weeks after my first COVID vaccine which was May of 2021. Long, typical, story short...After three ER visits, numerous visits to my primary care..two different Pulmonologist's Dr's, Pulmonary function test, Chest x-rays, cat scans..Cartiologist exam to include EKG with a Stress test. Having prescribed various inhalers, allergy medications, anxiety medications. No determination was made for cause and, nothing has ended the SOB. Every test came back negative for abnormalities. Basically..EVERY specialist has told me I'm in perfect health and, can not recommend any further testing. As you made mention, my SOB comes and goes. I am a very active person physically but, I have found it most noticeable when simply sitting or, after a large meal. I must admit, the one medication I have been prescribed which, genuinely has helped, is Pantoprazole for, possible, Acid reflux. Could our SOB be gut related ? I've viewed several articles that it could be the root of this problem.