Read around here! But looks like you're already doing that...
Sorry to hear about your bad grade -
You can DO IT!!!
Don't eat unless you are hungry. If you must have something to crunch on, eat some carrots or veggies. This one comedian who had teenage sons said "The way I could tell if my kids were hungry is if I had a cold, limp piece of broccoli in my hand and waved it over their heads and they were fighting each other to get to it - then I knew they were hungry" I try to remember that philosophy...
Whenever I feel like eating (same as you - I'm very mood based) I just think of eating a cold bowl of broccoli. That tells me whether I should eat or not.
I was just rambling up there. Just wanted to get your mind off your woes.