can't sleep

I used to go to sleep around 10. Now I sleep around 2 or 1 in the morning & not because I don't want to, I just can't! I'll stay up looking at my digital clock and watch as time goes by. When I cover the light that it emits & any other light source, I'm just up thinking & I can't fall asleep. Do you ladies have any advice on how to make myself sleep or make myself sleepy?