Too Tired

Most nights, I can NOT get to sleep. It's not that I'm not tired, I am SO tired, it feels like it's keeping me from sleeping. My parents don't understand why I can't fall asleep at night. Sometimes I wake them up in the middle of the night to ask for help, but they scream at me and call me selfish for waking everybody else up. I feel like screaming and tearing down the walls sometimes because its just so frustrating and nothing seems to work. Usually I just give up trying and I end up crying myself to sleep at 3 in the morning.