Social anxiety or... something. what do i do?

i'll start by saying that i've been like this for around five years. i'm currently eighteen so this all pretty much started when i was thirteen. that was when i started "going" to school online. now... i have no social life whatsoever. i rarely leave my house, and by rarely i mean maybe once a week literally. and that's only because i have to visit my dad(parent's are divorced) once a week. other than that, i never leave my house. i am ALWAYS in my room and on the computer all day long. i don't see my friends ever -- the only way i communicate with my friends is through texting(which i hardly do). also, i don't have many friends... maybe around 5. and i don't even know if i could consider these people "true" friends. i really feel like i have no one to talk to. the last time i actually saw a friend in person was months ago, and they came to my house to "visit". they only stayed for around 30 minutes. i get really, really scared to talk on the phone and go out in public. i get scared that people will judge me and i'm always scared that they'll make fun of me. i've applied for jobs but if i got an interview, i don't even know if i'd go because i get so nervous and terrified. i've avoided things before, important things because of my fears. i don't know what to do anymore. i feel like a prisoner in my own home, and i know the answer seems obvious: get out into the world, meet people, do SOMETHING. but something is holding me back. i just can't seem to do it. but i'm getting more and more depressed day by day. what do i do?