i will just put this out here.
I am suffering from this. and my doctors found that i have almost no iron in my system my hemoglobin is 7.2 supposed to be atleast 15.
when doing research it appears that a TON of the covid symptoms are related to the Iron metabolism getting broken.
without iron your blood cant circulate much oxygen, meaning just wallking up a flight of stairs changes my blood ox % from 99 to 75. it quickly comes back up to 99 but the heart rate from walking up a flight of stairs goes from about 95 (which is avg for me now) to about 150.
I hope more people will figure this out soon