I'm floundering too. Here are the things that seem to have made some improvements, but nothing quick and easy. Basically, all the stuff people say about being healthy, all the common-sense stuff that is so easy to blow off.
Eating well, reducing or eliminating processed foods.
Reducing or eliminating caffeine and alcohol.
Reducing carbs, keeping a steady blood sugar level.
Personally, I've not found increasing fats to be problematic at all.
Sleeping enough hours and doing what is necessary for good sleep quality.
When I'm at my worst, exercise is not merely difficult but seems to make me feel worse. But when I feel lousy but not at my very worst, activity helps. So I try to prioritize activity of whatever level I can tolerate, but when I have the "sensation" (hard to describe) that exercise will make it worse, I don't push it.
I had no reason to think I had a gluten sensitivity, but I'm desperate to try anything and I didn't see any risk of trying gluten-free for a while. I had a really big surge in energy for a while when I did it (plus my extra weight dropped off). I think it helped but it wasn't absolutely everything, unfortunately. (For a while I thought I'd hit the jackpot though).
Each of those things (except the caffeine and alcohol elimination since I didn't partake anyway) in its turn helped me in some amount. But none of them "cured" me. They are still worthwhile.
I don't have any "tricks" for bad days, and will keep my eye out for any suggestions. I seem to have this instinct that low energy can be helped by eating something carby, which technically works (albeit temporarily) under normal conditions but doesn't do a darn thing for me. Not even a temporary perk-up. And it may even make it worse. I've found medium-term helps (above list) but nothing short-term at all. On my bad days, I've not been able to do anything but ride it out.