I had the same problem for a while. My psychology teacher said to do the following:
- If you're really not tired, don't force yourself to lay in bed. Do something easy and light, like reading a book or listening to music. It will only make it worse if you lay there awake.
- If you go to bed and you're still awake 25-30 minutes after lying down, get up and do some light activities, as mentioned above.
- Don't eat heavily before bed or in the middle of the night; a light snack is okay.
- You should never do anything except sleep in your bed. That means don't read books there, do homework there, watch TV from bed... just sleep and nothing else. This is because if you do other things in bed, then when you lay down to go to sleep, your mind says, "time to read or watch TV" or whatever, and you won't be tired. By restricting the bed to simply sleeping, you're kind of training yourself to feel sleepy when you go to bed.

These things really helped me. Hope they work for you too! Good luck.