Why is my life like this and how can I fix it?

I don't live a regular teenage life. My life is full of doubts and depression and because of this I'm an antisocial person. The way I live my life is frustrating because I always overthink myself and I'm afraid to break my habits. I wish I could talk to girls, I wish I could be myself all the time, and I wish I could be more open to people. I'm afraid to break out of my shell. Seeing someone do something I can't makes me depressed. Can someone tell me why I life is like this