In my 'former life', when I was plugged into the system, I was a Registered Polysomnographic Technician. In laymans terms I diagnosed people with sleep disorders. By the sounds of it(going to school) you're in your late teens /early twenties. As such you require more along the line of 9-10 hrs of sleep. Our society and lifestyles being what they are, it is mighty difficult to get in that much sleep.
I would suggest go see your GP and get a referal to a Dr. specializing in sleep medicine. I can also give you a few tips to help you out in the meantime, but without a proper study, it is difficult to give concrete advice.
As such here are a few things you can do to help out:
1)Firstly, understand 70%+ of the population has insomnia at one or more times in their lives...so don't worry, you're in good company.
2)No caffiene at least 2 hrs before bed. Caffiene prolongs sleep latency for most people.
3)No vigorous physical activities just before bed. Many chemicals are released into your body from exercise that inhibit sleep.
4)As much as you can, try to go to bed at the same time each evening...your brain needs that routine to initialize sleep.
5) Also most people have a ritual they do before they go to sleep, like reading listening to music. This ritual signals the brain that 'it is now time to initiate the sleep process'.
6)If you can, no TV befire bed. TV generally stimulates the brain and that's not what you want just before sleep.
7)No alcohol before bed. Although 1 or 2 drinks will temporarily help you fall asleep, it REALLY screws up your sleep for the rest of the night.
There are a few other suggestions, but seeing a specialist is the way to go, if this persists for a longer period(weeks and weeks)
Hope this helps.
Cheers
Alex