Thanks for bringing this up, to me, sleep is an important aspect for fitness and beyond. We have a forum dedicated to training, and a forum dedicated to diet, but none for rest (well, i guess the lounge counts!).
There are many factors that could contribute to what you're describing. Changing bed/waking times, eating times, stress, depression, and environmental factors could all play a significant role. There are also more pointed medical reasons that may apply.
I have a difficult time with sleep occasionally, usually due to stress or some event throwing my schedule off. Some people like to workout before bedtime and claim that it helps them fall asleep after expending that energy. I'm the opposite; I'll be awake for at least 2 hours after working out. Then there are days where I feel like a zombie even though I got 9+ hours the night before. An intense lifting workout followed by a shower and a large, protein-rich meal usually help me sleep.
Your sleep troubles could be related to any number of things, so I couldn't really give conjecture on that without more info from you. Let us know what your afternoon-bedtime schedule is like.. that might have some clues right there. There are some resources that might help:
12 Tips for Better Sleep in Troubled Times
Additionally, there are supplements that may help sleep. Melatonin is very inexpensive and appears to regulate sleep cycles. ZMA (taken without calcium in the stomach) is purported to help produce a deeper sleep. Some people swear by the above supps, whereas I've only seen moderate effect, but they're worth looking into.
Try altering the temperature of your bedroom or adding/reducing bed sheets. Also, some people claim that having the tv/radio on helps them get to sleep. A sleep timer would be a good idea if you try this so that the noise doesn't prevent deeper sleep.
In short, try tweaking some of the above factors and see if there's any improvement. If not, I'd see a physician because it may be due to a medical condition.