Maybe it’s just the sheer strain of the pandemic and the time of year, making me slightly depressed.
Op, I think this the key.
I'm overall doing better in this lockdown than I was last time.
I've a good exercise & home routine, into wfh now, managing (just) with home schooling for 3 kids.
BUT
It's exhausting! I am running at full tilt all the time. I bet you're the same. I'm working full-time. I'm a single parent. My job is demanding (but I mostly love it). I'm desperately trying (and mostly failing) to progress legal matters relating to my divorce.
Some days I think I'm doing great! But I'll have a day where I'm nearly sick with tiredness the day after. I go to bed early & get up early to exercise.
But I've realised there are almost zero moments of downtime. I don't mean relaxing in a deliberate way. But the 'lost' moments where you make a cuppa in work or have a chat with a colleague. The moments on the way to work or school. An official lunch break.
Most of us are double-jobbing. All the spare minutes are crowded with home stuff, kids' stuff, chores, getting setting up for next day's work or school day.
I don't think we realise how important those interludes are, that happen naturally, usually.
I've no great advice, other than to recognise it & do your best!
(And yeah, double checking iron / thyroid no harm either!)