PLZ HELP!!!!!!!!!!!!!!!!!!!?

My mind's thoughts race constantly. I'm angry one minute and super hyper happy the next and sad/depressed. My anger is a very bad thing if your in the room with me. I punch, kick, threat, and yell. Happiness is no better I'm so hyper that I get yelled at for no reason. I'm just like what did i do. Sadness is the worst I think of killing myself I cry and cry. Throughout the whole day I think of killing my brother or mother. I'm super shy I can't talk to anyone. I'm not close to anyone. I have no friends to talk to. I have never had any friend I did once in K-4 but after that nothing. I NEED HELP!! I don't like talking to people I start cracking my fingers and nervous. I talk really quietly so u can't hear me. I'm 14 but I have been dealing with this for as long as I can remember. PLZ HELP ME PLZ!!!!