1. My perscription was out of date by two years and I let it go too long. My eyes struggled to compensate. Got it fixed.
2. For a while I had two different computer setups at different lengths, that contributed to it, they were different by almost two feet. Made changes to make them about the same distance.
3. My night computer I used in a dark room with no backlight. Added a single directed light facing the wall behind the monitor which gives it a soft but focused glow around the computer.
4. I'm PWM sensitive (see associated subreddit). I reduced brightness drastically on my phone and it helped alot with eye exhaustion since my brand is a well known bad source of PWM eye exhaustion and headaches.
After all these changes and a healing time of about a month, I'm back to being able to see individual pixels in text on my screens. My eyes feel like they have de-aged about 10-15 years and eye exhaustion almost never happens now, maybe once in a month and a half, after a few bad nights.
Other stuff that helped, improving sleep and restfulness and getting out and doing exercise more often. Also not using glasses when not needed.
Hope this helps!