Any coffee or the like? How well are you sleeping?
I know it's a bit 20-questions, but that looks alright to me so we could probably widen the search.
My first thought is that whatever is getting you down is draining you more than you think; humans ain't machines running off fuel but complex beings with powerful emotions, it might be that you need a little space and me-time to unwind. Also the work you are doing sounds pretty intense and if that is affecting your sleep you've got a vicious circle type thing
If it is to do with your food though, the only things I can think of to check would be whether you get enough iron, vit D or calcium. Maybe eat more of the same stuff? Like Kon sez, you might just be running a calorie deficit...