This has an amazing sobering effect: There's 7 billion people in the world. There's hundreds of trillions of organisms in the world. (This one website said 10,000,000,000,000,000,000 of JUST arthropods). Not only that, but there's been waaaay more organisms that have lived in the world before us. If you think that you have an equal chance of being born as any of those organisms, and yet you were a human, you've just won the mega-super-lotto. Really. I assume you live in the US, which means you live in extremely good conditions. You are sooo lucky, so don't be ungrateful. That doesn't solve your problems, but just suck it up and live. You're a human and strong and wonderful and perfect, so be happy!
TL;DR: You're lucky, don't be ungrateful. Your problems are insignificant in the grand scheme of things. You're perfect so don't sell yourself short.
I have been dealing with depression and to help me I have watched funny movies... Bloopers, and Just look forward. Life gets better. I have also reached out to one of my friends to find that she has depression... So we help each other through it. Teenage years are the hardest... so I have been told. And for insecurities just love yourself. Not too much though... That would be called Narcissism and is frowned upon by most people.... :P