Apart from great comments already posted, please read about "long covid". I'm not sure if it's officially recognized yet but it's a strange illness lately and a large number of people suffer from it. One of most important symptoms is chronic fatigue. I'm fighting it since last year and one thing I can say is that the fatigue is different from anything I experienced in my 43 year life. It's crippling and even getting up requires effort. Caffeine in large doses helps somewhat but only to an extent.

There's always been a "post viral fatigue syndrome" with many other viruses and it is a known phenomenon, maybe it's just a similar thing with Covid. Only it affects much more people I think. And most importantly you can get it after asymptomatic Covid, so you don't even know you had it.