I don't know what's wrong with me?

Hi this may just end up as a rant but I'm honestly starting to think somethings wrong with me. I used to go out every day and be social with everyone. I'm an easy person to talk to and people seem to open up to me pretty quickly. The thing is.. I dont really open up to anyone. I know everything about everyone but nobody knows anything about me.. and I feel like I have no one to talk to. I live with my mom and see my dad once a week. My dad points out how im always "depressed" or upset and he admitted to me that he worries about me. He's asked me if was going to kill myself before, I'm not even kidding. But hes actually supportive and I enjoy being around him even though sometimes we get into arguments. But my mom on the other hand.. complete opposite. I have 2 siblings, one almost 30 and one is mid 20s. Oh, I should probably mention that I'm 17. But my mom treats my siblings perfectly as if they do nothing wrong. She goes away most weekends with her boyfriend and I usually get into arguments with my sister while she's gone. Lately I've just been pushing everyone away and I've stayed inside the past 2 weeks and just sat in my room. I dwell on the past A LOT and I can't control it no matter how much I try. I'm always upset or even when I'm happy, all I have to do is think about something sad and I'm like that the rest of the day. Sometimes everything hits me at once and I randomly break down. I hate showing emotion to other people because I feel weak. What do I do?