What an awesome post! You are mature beyond your years.
Soccerchick, just your screen name tells me you are at least interested in being active, so start there. Walks, runs, (skips, hops, and jumps count too), anything to keep your body moving. The diet part is very important, but at your age developing an active lifestyle that will be part of life, for the rest of your life, is the very best thing you can do for yourself.
Feeling anxious or blue? Take a walk around the block or over to park if there is one nearby (just don't stop at the 7-11 on the way home
). Join a group - sports would be great - but even a group that helps others less fortunate, or that make some sort of contribution to your community will help you feel like you are a part of something bigger that just you.
And as Tamara says so clearly, give yourself a break. As you know, being all down on yourself only makes thing worse. Start with small changes and build from there.