I also have had the battery of diagnostic testing. With the exception of a Tilt Table Test resulting in a diagnosis of Postural Orthostatic Hypotension, all have come back within NORMAL range … blood tests, chest x-rays, ECHO, Cardiac Stress Test, Pulmonary Function Test, Chest CT. Scan.

T-cells have the longest “memory” over antibodies, so you have a greater chance of getting a positive test result with this where the window is very limited with a PCR or Antibody test. I got my t-cell POSITIVE almost a year after symptom onset. Since I’m presuming an initial asymptomatic acute COVID case, I have no idea how much time had lapsed since my COVID infection.

Link to T-Detect website to order t-cell test:
https://www.t-detect.com/
I hope you get some answers and good guidance to get you on the road to a swift and complete recovery.