Rain, I'm 28 and still struggle with this issue(not to say that's normal).
But, one thing you shouldn't get too down about is doing things that other people do. You don't have to be a xerox copy of someone, but you should also acknowledge that you enjoy something when you enjoy it. So you have to kind of step back from yourself and say "I like this movie, and I don't really give a sh** that so and so likes it too, or that they showed it to me." At the same time, don't passively tag along. If you're with friends or whatever and you're all watching a movie and you dislike it, be like "damn, this movie sucks."
It's perfectly natural to be introduced to things through other people, so don't alienate yourself when you like something just cause someone showed it to you.
At the same time, don't be afraid to get lost in your own interests. They're there, you're just not listening to them because you feel you need someone's approval. Especially at such a young age, it's important for you to take those time/energy investment risks and find out what gets your juices going. Don't be lazy. It can be somewhat arbitrary, because maybe you're curious about alot of things. Maybe you like music alot. Well, go get a guitar and say, I'm going to try this out for 3 months. Then scrap it if it ain't your thing. etc., etc.,
Anyway, good luck, I know how you feel. Just got to find a balance and be true to yourself no matter who likes/doesn't like you. sh**, look at an celebrity, you have a million people that adore that person and a million people trying to tear that person down. The bottom line is, you have no choice but to be yourself, and when it comes down to it, you're the only person that has to live with you, so why not make yourself strong and happy.