Feeling withdrawn and depressed?

I've never really been close to my family, and all through elementary and middle school, I sat alone, had little or no friends that I talked to outside of school, or interacted with. Everyone liked me, but I absolutely hated everyone. My friends and I have little or no emotional attachment, and from about the ages of 12-16 (I'm 16 now) I just sat on my laptop alone in my room. I used to still be able to fake it around people, or was actually genuinely happy. I was more active and interactive with and around people in social settings, but at home, I was bored, alone, and miserable. I was in therapy last year, and they said I had mild depression, and by about 3 months, they had said I had severe depression. I refused any drugs they offered me though. This summer, it started out great, as I was living with my sister and her boyfriend and we all got along, and I finally felt a sense of security and had a real home. But then they broke up, and now I'm living with my dad, his girlfriend, 2 step brothers (17 and 7 years old) and my step sister (14 years old), and living with a family of strangers doesn't help me at all. I still just sit in my room alone all day on my computer. I hardly smile, laugh, or really do anything. I see my friends and my girlfriend constantly, but now in social situations, if someone says something to me, I fake a laugh and don't really have any reply to anything anyone says. Everything just feels so awkward, and I'm at a loss for words. I've had 3 suicide attempts, they called the suicide prevention on me at the probation office my mom took me to when she found my friend and I smoking weed (she knew about it before, though) and they made me roll up my sleeves and counted over 200 cuts on my arms, although I've stopped that now. I thought everything was better, but after I moved in with my dad, I just started to feel more withdrawn each day. I've had a lot of drug problems in the past (but now only smoke weed), and I'm sure my outlook on everything is much different than the average persons because of it. Although before the drugs, I still saw things differently than everyone else my age, and always hung out with people much older than me. I'm sorry for the story, but I'm not sure how anyone can help without knowing the situation at least a little bit. I just want to know how I can be more outgoing around people again, so I can have normal relationships with people. I can't say I've really had a terrible life, I've just always felt different, and it's made me lonely and withdrawn. I'm not really sure how much longer I can stand it, and I cant imagine any way to fix it. So if anyone knows the feeling, or can help at all, please do. It's much appreciated.