You might just need to ride it out while your body adjusts. How are you sleeping? I would imagine changing your shifts is a bigger reason for the brain fog than changing your diet.
I would keep eating at regular intervals (breakfast/lunch/dinner) and emphasizing fat and protein. I wouldn't go too crazy on caffeine, especially closer to night time. Also, don't try to do too many things at once and give yourself a break if you feel to run down - don't force workouts. If you feel the need to cheat for your psyche's sake, go ahead, don't make it too crazy, but maybe giving yourself a small psychological break from this new way of life could be beneficial. Good luck.
I used to seriously post here, now I prefer to troll.