Don't use any substances to assist you because you might become dependent on them to fall asleep. You need to re-establish your sleep rhythm by going to sleep at the same time each night.. say 10 or 11 pm. This will train your body into a new rhythm. It won't be easy at the start because you'll perhaps feel right awake. It's important that you begin to "wind down" before you try to sleep. Don't drink anything with caffeine, don't eat anything, don't do anything that will engage your mind a great deal. A few weeks of this and you'll hopefully have a reset sleep rhythm.