If you're not allergic to milk, then the best all natural sleep aid is a warm glass of milk.
I find that when I can't sleep I warm up a glass of milk and drink it and within about 10 minutes I'm able to drift off to sleep.
If that doesn't work for you then you can try some melatonin and Valerian "Valerian" is a natural herb extract that helps people fall asleep faster and get improved sleep at night.