Suicide was described to me in school as a permanent solution to a temporary problem. It's like completely sealing a door in cement that squeaks, if you would just put some WD40 on it, or figure out what's causing the squeaks and fix that, then you wouldn't have the problem.
Suicide is something a lot of people consider, but they don't realize that what they're considering is death, and not the act of killing themselves. While you have the right to do so, and your decisions are your own, you must decide if it is truly beneficial to do so, or if you could benefit more by doing something else to fix your situation.
Make yourself feel less trapped, don't let yourself get down, don't think about things that make you sad, just do them and be done with it. It's really hard to live, it's one of the most difficult things anyone has to go through, especially if you're in a tough situation.
Getting help isn't always the best option, a lot of the times those people can make the situation worse. Most of the time, you just need someone who you can talk to that listens to anything you have to say, and is generally interested. Try to get involved in big brothers big sisters, or something community. You may not be outgoing, but the idea is to take your mind off of such thoughts, to give you a reason to live, and something to look forward to.
Really, that's it. You feel trapped, you feel lost, you feel that there's nothing worth living for... you feel dead already so why not end it? That's the kind of thinking that leads to suicide. If there's an inkling in you that says you don't want to die, then do everything in your power to find something worth living for.
If you honestly can't, truly have no reason for living, then see if you can't give it some time... a few years... if something changes, you saved yourself. And that's a great feat of strength right there.