Depression is a very serious issue and you need to see someone about it. It's difficult to suffer in silence and cope alone. A lot of stress, whatever they may be, can build up and cause many long term health effects. As you have already noticed, your sleeping pattern and appetite, as well as weight are all being affected.
Talk to people you trust and confide in them. A friend, a family member, a teacher. Anyone you feel you could tell and who could help.
Find out if your school offers counselling service and book an appointment. If not, contact your local doctor and see if you can referred for some counselling. Tell them about your eating issues, as well as sleep and stress. Tell your teacher about all the stress and ask for some leniency, if possible. Some room to breathe and compose yourself.

To deal with some of the stress, I'd suggest you take up exercising. You'll reap many health benefits, helping you to lose weight as well as release endorphins (feel good hormones) into the blood stream and feel a lot more relaxed.
For sleeping, you need to set yourself a schedule and stick to it. Make sure you get at least 8 hours of sleep a night. A lack of sleep can badly affect your mental health.
For your eating issues, make sure you eat three square meals a day and most importantly, make sure you have a health breakfast.
In the meantime, it may be a good idea to start writing a diary, so that you can openly vent your feelings. With it, you could draw a food chart, as well as track your sleeping. You could present all this to the doctor or counsellor, to give them a better insight into what's going on.

Good luck.

Posted at 8:32 pm on Aug. 12, 2008