I too don't fall asleep easily at night. In my case, my mind simply isn't tired. So, when I lay down and try to sleep, I obviously can't fall asleep. Even if it's 2am or 3am, often I can't sleep.
When I worked evenings, I was OK, cause usually I get tired around 5 or 6 am and fall asleep fast.
What I've found that works for me to a point where I can actually show up on time, and be awake at work ....
Melatonin ... a little bit around midnight, usually I get to sleep by 1ish and sleep a solid 6 and 1/2 to 7 hours.
Benedryl .... I am drowzy and feel like zombie for 16-24 hours
I've talked to my doc about it, and he said he thought it was a late sleep phase issue. Would need to do a sleep study to "confirm" it, but with melatonin ... I feel like I've got things under control as I am now able to fall asleep by 1 or 2 am every night.
http://en.wikipedia.org/wiki/Delayed_sleep_phase_disorder