Do you have a steady and consistent eating and sleeping habits?
The human body craves consistency (going to the bed at the same times every night, waking up at the same times, eating at the same times) When you don't have a schedule, it wreaks havoc with your biology.
This is all tied to your circadian rhythm (the biological clock that controls your sleep/wake cycle)
Bright computer/television/telephones screens emit light in the blue wavelength of the spectrum. When blue light hits your optic nerve it makes your body think it's still day time and your circadian rhythm doesn't cue to release melatonin, and other associated chemicals to make you feel sleepy.
I use a free PC application called "Flux" which changes the colour temperature down to 2000-ish K (which blocks out all blue spectrum light) It's set on a timer synced with the sunset sunrise cycle at your location.
If you have an android powered phone, download a free app called "twilight" which does the same thing too.
If you are really struggling to get to sleep, you can even go as far as to buying special glasses/spectacles/sunglasses that serve the same function. You can also buy special light bulbs to replace your reading lamps with, that also don't emit blue spectrum light.
Good luck! I can vouch for all these methods, they helped me get to sleep much earlier than i used to