Have you been tested for an under active thyroid? such a condition really affects energy levels, although when that specifically comes up on GN as a topic, some of us who have the condition and are prescribed thyroxine for it, don't necessarily feel our medication is a silver bullet as far as giving a boost to energy levels, but maybe ask your practice to test you for that along with any other recommendations here. I drag myself off to the gym a few times a week primarily to go on the treadmill, I know I can build up more of a pace on that, it's really boring though, of course walking in the open air, especially in when the weather is nice is better, but I've been super cautious since breaking an arm on one such walk, I feel safer on the boring treadmill. I make sure I have air pods in and something to listen to, it makes it more bearable. I do a few load bearing exercises as well, I get no enjoyment out of any of this and don't particularly feel energised afterwards, I just feel it's something I have to do, I know also I need to lose a few pounds, weight gain was something that kicked in with my under active thyroid diagnosis and I've been fighting it ever since. I try not to eat bread before I go to the gym, I've always found there's a spike with some carbs in feeling really tired afterwards. My doctor advised a few years ago, that I was deficient in Vitamin D, so I religiously take one every day.
Your post resonated, some days I'd give my right arm to have a modicum of vitality, you're not alone, not much of a consolation I know.