Stop being so scared

I hate being like this.
Everytime I leave the house.. I feel nervous.
If I go into a public place, like a shopping centre, I even start shaking sometimes, especially when there are a lot of strangers around.
I’m ‘scared’ of trying new things, because I fear drastic changes. I don’t have very many friends; trust is an issue.
I’m scared to open my mouth to say something.
I can’t hold down a job, because I’m not ‘talkative/social enough’. I sit alone, practically every day. I hardly ever get phonecalls. People don’t even bother trying to talk to me anymore.
I am only seventeen years old, and I want to overcome this.