I guess the real question is, "Who am I?"
If you have confidence in yourself, it doesn't matter what other people think about you. If you are happy being you, then you've got it made.
But if you feel like your life is worthless, find out what you think will make you feel useful and then go and do it.
For example, I feel useful when I help others in their lives from my personal experiences.
If you feel no one understands you, it's either because you don't understand where other people are coming from or sometimes that's a form of self-pity... and it doesn't mean you're a bad person, it just means that you don't have confidence in yourself.
Be proud and happy to be the person you are, because there is someone out there who will understand you. I promise.
I have no idea if that helps... but hopefully it helps a little...