A couple of questions I would ask:
Are you eating enough? If you’ve dropped you calories drastically this could explain the fatigue and lack of recovery.
Is your diet balanced? Don’t fixate on eliminating particular things but are you generally eating a good balance of healthy carbs, proteins, fats?
Are you drinking enough water?
Are you sleeping enough? I like an afternoon nap too – nothing wrong with that.
Are you sitting for most of the day at work? This is the number one reason that affects how I feel – since lockdown and constant TEAMS meetings I really feel it in my hips and back etc. Need to consciously get up and move.
How is the mood/mental wellbeing? – this can really affect motivation and perceived energy levels.
As a 40 year old who has had a pretty active life and fallen off lots of bikes and spent a lot of time lifting weights I would say I am always slight sore for one reason or another – either chronic or acute. I am sure the sitting all day doesn’t help.
The increase/change in day-to-day resting heart rate is strange – mine definitely goes up when I am busy/stressed at work and some of the other issues above are out of whack. But it usually normalises pretty quickly too.
Have you spoken to your GP?