Uncomfortable with people

Well Im an 18yr old female.
I started being uncomfortable with people when i was around 15. I slowly stopped going out with friends and became more withdrawn. I was always down and stressed and for a time hurt myself. I stopped doing this and things got better but i lost some friends.
Over time though ive become more withdrawn and now rarely leave the house and only have 1 main friend who i rarly see now that school is over.
While I never saw this as much of a problem, Im starting a new school now and know no one there.
Ive never been good at meeting new people and now want to start working on my problems.
I cant seem to manage small talk and get really self conscious when talking. It ends up in an aquward silence. Even the idea of meeting new people has me anxious as im afraid no one will like me, will find me boring or ill do something stupid.
I dont know why i feel this way, and i seem to be getting worse. Ive never talked to anyone about how i feel and i really dont know why i act like this.
Im now tired all the time, I oversleep and Ive have lost interest in lots of things I used to enjoy.
Any Advice??