i'm at 56 days sober, and i think i know exactly how you feel... i slept great at night, but still i'd get hit by a truckload of deep exhaustion every single day. i'm just kind of gettinf out of it... i didn't get it today, but i did yesterday. i'm definitely feeling improvement, but i still get hit with that exhaustion sometimes.
i've been asking about this, as well... and from what i've gathered this exhaustion is not uncommon. i'm just trying to rest if i can at those times it hits me bad. i understand that it gets better!! i would say though that if you are concerned, talk to your doctor. better to treat our bodies right while we heal!!
best wishes to you, GJ.