I hear you and I believe you. I was a runner, worked out regularly and perfectly healthy until my first Pfizer shot. It sounds like you might be Experiencing Post Vaccination Syndrome. The post exertional malaise is one symptom of it. The SOB I got immediately along with dizziness and daily crashes for hours. Nothing showed up in lung X-rays or pulmonary testing. Do this:
Get your ANA tested
Check for Dysautinomia
Check for POTS
There could be an autoimmune component to your SOB
Do you have heart palpatations? Tachycardia?
After being healthy, taking the shots caused my immune system to go haywire. I now have PVS; Lupus SLE; Sjogren’s Syndrome; MCAS and POTS. So look these diseases/Syndromes up because the research is showing that many people have all these diseases and more triggered from the mRNA vaccine.
You have to keep pushing for answers. Regular scans of your heart and lungs will only show normal then your dismissed which is more than annoying. Look in YouTube and explore these diseases and see if they fit then ask your doctor to refer you to a specialist in the area!