Speaking as a sufferer of chronic depression
, I know what you are going through. You are having a major depressive episode, it sounds like: lack of sleep, appetite, the crying, being tired in class.
So here's what you need to do: get help. There are medications that are quite effective at dealing with this, as well as psychotherapy. You need a professional to figure out what is causing your depression. When you get treatment, you realize that all of these things are just your brain fucking with your mind, and the greatest hope is in realizing that there is something you can do about it.
Did you go away to school? Somewhere with less sunlight? It is very possible you have Seasonal Affective Disorder - especially since you are having this depression at the darkest time of year. There are very easy and effective treatments for SAD.
Please, please, please, get yourself into whatever counselling/health services that your school provides. And remember: It's your brain chemistry. You don't have to feel the way that you do. Try to get some hope out of that, and keep going, don't give up on life!
It does occur to me that you could be a troll
, but this is something too important to fuck around with, so I will take my chances of looking like an idiot. Because I know the sort of things you think about when you are in this state, and I don't want anyone to go through what I have many times in my life.