I'm always deppressed?

I used to be a loud crazy person and got along with everyone. I had a huge fight with my mates- good riddance. They never used to treat me right. People have been coming up to me this whole week asking me why am I quite why are you so sad. I just pretend to them and say I’m feeling really sick or tired. Sometimes being by myself overwhelms me so much at school I feel like crying. I'm never open anymore. My 2 ex best friends do talk to me occasionally and that's if they are by themselves. I don't really miss my other friends as I always felt like a tag along but now I always look like a depressed git. I hang around with a new group but I still feel left out. They are nice to me and I do like them but i still feel sad and lonely with them. Sometimes they confer and whisper to each other and when i ask what they are talking about they don't tell me. This whispering carries on for 2 periods and when it's break they tell me to come with them; they still do it. When they ask me why I am quite i tell them i feel left out. They just look at me and tell me not to worry and you'll feel better in a couple of months. I've stopped going on the bus (I walk it now) and I’ve even stopped going to the shop and I’m literally the first one there. Now when you look at me in the corridor I always have a frown on my face but before you'd see me laughing and smiling. I don't know what to do I feel crap all the time and feel hated and a waste of space. I’ve never hated school but now even hearing the name I feel sad. If I tell my parents this they'll get worried and I don't want them thinking about me and worrying about me every day so I keep this to myself. I feel like if I tell anyone they'll think I’ve got paranoia or I’m crazy. I’ve quitted facebook and no one talks to me on msn. I eat and sit with myself at lunch. Please help I would love any advice to stop me feeling this crap. Thank you.