It's probably work related, it used to happen to me. I found that putting a really boring video or DVD on to watch in bed put me to sleep half way through!
A bit of exercise is a good idea, too. It's not the weather now for evening walks unfortunately. Definitely no tea or coffee after 6.00 or 7.00pm. A glass of red wine isn't a bad idea. There are also relaxation tapes, which I found excellent but they are much more a "woman" thing than a man's.
Talk and see if you find out if there are any underlying worries, not just normal work stress.
A good massage can also help a lot.