I find it starts off this way, when your body isn't in the rhythm of exercise. As you exercise more your body changes, and its response to exercise changes.

When I was exercising 5x a week, for months, the exercise routine was energising.

When I did nothing during months of COVID, I gained weight, felt lethargic and found exercise draining.

I was 3-4X a week at the gym. Weights plus HIIT for over a year before covid. Nothing. Didn't help my sleep, didn't slow my weight gain, didn't boost my stamina in daily tasks. And layered on muscle soreness.

Sounds like you weren’t doing the right things in the gym. Which is fine if that’s not your thing, but your quality of life will suffer to not have a fitness component.

This could be a hormonal imbalance, such as your thyroid. Most people (eventually) react positively to such lifestyle changes, unless your biological machinery is off the rails.

That's what I thought. I requested a load of blood tests but doc didn't find anything.

I felt the same way until I tried weightlifting/strengh training.

Running, biking, swimming just left me exhausted and I hated every minute of doing it.

Strength training makes me tired and sore and while it's not great fun to do, it is something I have been able to stick with for a couple of years.

Some people love being physically active, I have never been that type of person. I will never "love" working out. But despite that, I have found some exercise that I am able to do habitually. Keep trying.

This sounds silly, but: do less. Run slower. Do 3 pushups or whatever. Whatever you can do consistently is going to be better than doing more for a bit and then quitting.

Not bad advice. If you can do 3 pushups today, do it. Then do 4 tomorrow. Then 5. and so on. Or run for 5 minutes, then 6, then 7. Whatever you are able to do, add a little bit to it the next time. Not so much that it's a barrier. Just a bit more than you did last time. If you can stick with it, in a year, you'll be amazed where you are.

Have you done it multiple times a week for more than 3 weeks?

I've done it daily for 8 months (P90X). Still hate it. Still doesn't "recharge" me or do any of the other things fans claim it does for them.

Do you at least sleep better/rise easier?

I've done every possible combination. HIIT, free weights, bands, VR cardio, lengthy strolls. I've done each for at least months at a time. None of have had any noticeable effects on my well-being. I live in a big city with no car, so I walk a lot no matter what. Even going relatively hard on barbell squats and dead lifts just made my legs feel weaker.

Your body is surprisingly good at feeling how it expects to. If you expect to feel refreshed, you might. Learning how to control your expectations to suit your goals is a bit of a superpower, but it's one you learn by practicing it, not by talking about it on the Internet.

Keep in mind too that everyone is different, don't just accept random advice from strangers online about your body.

If you truly just become more tired from working out, and you're working out sensibly, then you might have a condition affecting circulation or your heart.

Exercise doesn't have to be a full-on "workout". Just going for a walk around the block can be enough to refresh you and break the sort of inertia of sitting still.

Yes, anything is better than nothing.

Lately, 5-10 minutes of yin yoga and 20 minutes of walking is what I can prioritise.

Just having a walking break during work is great; three people at my office do that.