Help?

So sometimes I have a great week or so of eating healthy and the right amount of calories and exercising. Then, out of the middle of nowhere, I have a day where I get enough sleep but still feel exhausted, my thinking is foggy, and I am super cranky. It feels like I have low sugar, but if I eat a lot of healthy food, I don't feel better. The only thing that makes me feel better is binging...but that's obviously not good for me! Does anyone know why this would happen, and what a better solution would be? And it's so hard sometimes to just ignore that feeling when I have classes, tests, etc.