I don't know what's happening to me

I've been having these weird episodes where i have no control over myself. I scream, as loud as i can, i cry and it feels like I'm being controlled by someone else. I get angry; very angry. I've been trying to tell my parents about this but everytime I bring it up, they just say that it's all in my mind and that i should try being more positive. I wish they were right. I just don't understand how to be positive when i have absolutely no control over my mind. I need help. Today, another episode took over. I went up to the terrace and i screamed as loudly as i could. I didn't know what what was happening. I started crying and i wouldn't stop. I tried to throw stuff off my terrace and then i ran upto the frontyard and sat on the ground for about an hour and kept talking to myself. I calmed down a bit. I came back inside the house, where i took a shower, relaxed for a bit, but then my parents came to me and started screaming at me. They told me how ungrateful and selfish it was of me to cry. They told me that all i do is ruin the atmosphere and cry. They kept going and scolded me, but never asked if i was okay; if there was something i wanted to share. Never. They don't let me cry and expect me to pretend to be all rainbows and smiles when i'm not okay. I'm not okay and i need help. It's not for show. I genuinely need help. I don't know what's wrong with me or why i'm being this way, all i know is these episodes have affected my performance at school, my relationship with friends and i don't know who i am anymore. I just want to know what's wrong with me. It's hard to sit down with your feelings when these episodes keep caving in. It's so hard to think about anything. All i wanted to do was let it all out, but i had no one to talk to. My parents turned their backs on me. My friends don't listen. i don't know what to do. I just need help.