Some great advice, already. And you're absolutely right about just having to keep trying different thing until you hit on what's right for you. Often sleep problems are due to some underlying anxiety - thoughts keep running through your head and you have a hard time relaxing your mind, even if your body is relaxed. Just like we suggest with babies, it's a good idea to have a bedtime routine, that prepares your mind for sleep. Make sure you have no high stimulation activities before bed, and try to read something just before you lay down. Once in bed, do some breasthing exercises (Kate described some) or you could try progressive muscle relaxation (let me know if you want more of a description of this). This will hopefully just relax you, if not put you to sleep. Then, try not to focus on anything (especially not the clock!). But if you're still awake after about 45 min to an hour, and not getting sleepy, you might want to get up, leave the room and go read quietly until you feel sleepy. Then try again. The worst thing to do is lay in bed, tossing and turning, waiting for sleep - it will only start to stress you out!
But I would suggest you really look into your current thoughts and worries to see if there's something bothering you that's preventing you from relaxing. Problems or frustrations with dh? Worries about the kids? Low mood? There is usually a reason or a combination of factors that cause sleep problems, and once you find out what, you can really make some progress.
One last word about chemical sleep aids - even though they may work in the short term, they are NEVER a good idea to use indefinitely. Most sleeping pills don't actually gives you normal sleep (the right amount of REM and deep sleep, etc) and when you go off them, you're right back where you started, unless you've found out what the underlying problem is.
Let me know if there's anything else I can do to help - I know how hard it is to be unable to sleep!
