I'd recommend seeing your GP. I've had quite severe sleep problems, leading to me being sleep deprived the majority of the time, and this combined with other issues led me to being prescribed melatonin tablets, as melatonin is the hormone which induces sleep, and I clearly lack! Since being prescribed these my sleep has improved drastically - I'm not saying that you need them, because different people need different treatments, I'm simply saying there are things your doctor can do to help.
However, there are also things you can do yourself to help yourself sleep:
1. Don't eat in the hour before you go to bed, as your body will still be digesting the food, thus keeping you awake
2. Try not to use your bedroom for watching television or doing homework, as separating yourself from these things will allow your brain to switch off
3. Find something that relaxes you to do before you go to bed, i.e. a nice bubble bath
4. Try reading or listening to calm music before going to bed to relax yourself
I hope this helps,
Feel free to ask for any more tips