There are a ton of factors that can cause insomnia. How stressed are you? Are you worried all the time, do you have anxiety attacks, etc.? Are you depressed? Do you have any medical issues that may prevent you from sleeping? Is the room your sleeping in at a comfortable temperature? Is your bed comfortable? Do you have anything around you that disrupts you during the night? Have you recently had something happen to you that may have caused trauma? Is your sleeping schedule consistent (I would say this is the biggest one)?
Just because you can't sleep doesn't mean you should pop sleeping pills. Sleeping pills should be last resort; if you've tried everything else possible and nothing is working.
I used to have sleeping issues and I used to be tired / fatigued a lot during the day. I worked 2 part time jobs for 5 years. My sleeping schedule was so off because my hours varied so much. Some days I had a hard time falling asleep, even if it was 4am and I was tired beyond belief. It wasn't until last year when I started my full time job (working 7-3:30) that I finally had a consistent sleeping schedule and I could finally fall asleep every night comfortably and easily. Usually I am out like a light bulb within 15 minutes, from the time I lay down.