Hi.
Are you a teenager? Even if you're out of your teens, I'm impressed that you're submitting stories to magazine and publishers. It's also kind of extraordinary that several of your friends are published. Sometimes it takes dozens of rejections before even the best writers get their work accepted.
What I'm saying is that I think you might be measuring your writing success against some pretty untypical circumstances--and being too hard on yourself.
Your letter seems like it's about more than writing, though. When you say you're "not particularly good at anything," that's a pretty broad sweep. And the way you bring up depression and death makes me think that it might be a good time to see a counselor at school or somebody you can speak to in confidence about those feelings.
As for the writing, if you're serious about it, my advice is to try something completely new and different to get yourself out of this rut. Is there a class you can take outside school? What about trying a whole new style of writing or reading a book about the writing process?
I also recommend giving yourself a little bit of a break about all this, however, and maybe even treating yourself to something special! Besides relieving some of the pressure you seem to be feeling, focusing on other things could be a good way to remind yourself about things in your life that give you pleasure--and that you may be "good at." Not to mention that it might just put some sparkle into your writing.
Meanwhile, you might want to check out these resources about depression.
