Why can't you sleep - is it because you are lying there worrying about not being able to sleep - try putting a radio your bed - turned down low enough not disturb anyone else in the house - listen to a talk show - concentrate on that not on the things going round in your head.
Paint a picture, plan the layout of a garden, imagine you are lying on a beach with the waves lapping on the shore and the sun just gently warming your body - do anything you enjoy doing in your head, gradually your thoughts will turn into a dream and you will have floated off to sleep.
All of the above cost nothing.