i too have extreme fatigue . finished 6 month chemo , mastectomy , 3 weeks radiation in june last year . got covid in dec had antivirals recovered well . but if any activity one day would have to rest the next . could spend all day in bed but don't wish to get worse . sooo tired all the time . only way is to have coffee which before i could not tolerate . feel like getting more tired over time . but i'm in my 60 s so that may be reason also . on exemestane daily. but just over feeling so tired . But any exercise i do after i feel such a huge boost of well-being like my body is saying yes i need this .

i think all your personal challenges and grief would play a big part in your exhaustion too.
i feel all you can do is take one day a time, indulge yourself ! your body has been thru a lot and mental stress is terrible . try go outside each day even for a short walk .it will make a difference get a pet . a little kitten or something for company. what you are experiencing is normal ! you've been thru the wringer !

try find a good tv series to watch, something to look forward to , a book , play some music . if you can try find a Tai Chi course be perfect , it's gentle exercise .

and don't expect too much of your body, rest and heal at your pace . you deserve every indulgence at this time , it's your time to heal .
all the best !!