They do ones to help you sleep rather than the normal Kalms to calm you down ones.
I've used them and find them very good but it's not good to use anything like that more than just short term.
Have you tried things like camomile tea, sleep sprays/lavender, Lush to a temple balm, making sure your room is dark enough (darker curtains or an eyemask?) and at the right temperature etc...
I used to find relaxing music helped, especially classical, or listening to something monotonous like a news channel (though you're stuffed if something big happens!), relaxation exercises or CD's?
I used to do an exercise where I got comfy and bit by bit imagine each bit of me tensing then relaxing and try to let my mind drift or, if all else fails, daydream rather than think of real life stuff. I try to concentrate on rest and relaxation rather than obsess about sleep.
Some relaxation or meditation classes might give you some ideas.