I am about 3 yrs out and really get that "exhaustion" thing too. I really need to nap each day. It is tough to fit in with work, etc. My exwife didn't understand why I was sleeping. My new girlfriend understands fortunately. Your brain gets into a fog.
I have started to do the following. First, the brain only uses simple sugars for energy, nothing else. It wont use carbs or fat.
So what I do is the following: I never ever drink any soda at all. Then, on a day I am doing a long work thing, I bring a 2 liter of mountain dew. It is loaded with sugar and caffeine. Also, because I never drink it until a work day it has more of an effect.
I work around 3 days a week.
I had a day a month ago when I was driving a long distance (4 hrs) and I literally stopped and bought a hotel room for a nap. It felt ridiculous paying 60 bucks just for a nap, but I knew if I kept driving , I would wreck.
The brain sometimes gets in a fog. Oh well. Thanks for your story and I hope you feel better.