Why do i feel so lonely and sad?

Hi. I'm 14 and I have great friends at school. They are all very nice and we all get along fine. I don't go out much but i'm fine with that. I like spending my time indoors. Also i talk to my friends over XBL or on Facebook after school sometimes. I don't see members of my family a lot except for my mum and granddad. I'm also very shy and nervous. I sometimes think about wanting a gf maybe but i don't fancy any girls in my school. They're all into fashion and modern teenage stuff unlike me. I'm a bit more mature than other boys in my school and i'm also very creative. For a while now I've been feeling lonly and very depressed. I don't know why though. I feel like I'm not good at anything and that I've wasted most of my child hood but i don't know why. Why do i feel so lonely and sad and what can i do to cheer me up?