Could be the low carbs.
Could be a lack of certain vitamins/minerals (Magnesium for example).
Could be your sleep habits.
Could be 10 other things or a combination.
It may sound counter-intuitive, but I force myself to wake up at 4AM most days and it has actually made me more energized throughout the day. I think it’s because I sleep more soundly at night.
If you play video games especially fast paced shooters (like COD), avoid them at night. They’re too stimulating. It took me about 4 years to figure that out…
I also avoid lifting at night. It took me a while to figure that one out too. I would fall asleep quickly, but toss and turn after about an hour or two. I used to pace around my damn house at night because of it. Weight training at night is just too stimulating for me that’s why I lift in the AM now.
My $0.02, the above might not work for you of course.