I have the same fatigue and lack of energy issues due to 3 cases of Covid. I have had virtually every potential cause tested for with no answers. I have quizzed my NIH admins and docs and they all say the same thing- “we don’t know”
I consulted my GP who did more tests and , again, couldn’t find any legitimate causes. He labeled it Cronic Fatigue Syndrome and suggested scrutinizing my caffeine and sugar intake as well as policing my diet. He also prescribed low dose Adderal in the morning to jump start my system. It seemed to help but I don’t want to rely on a drug that may have long term effects so I am now concentrating on exercise and diet and it’s seeming to help a bit but not great.
Frustrating to say the least but again, all the researchers are telling me that these symptoms are appearing to slowly go away in their study subjects. The ferocity of the Covid virus attacks the immune system in a much stronger way than other viruses, and takes longer to recover.