Some people find writing down whatever is bothering them can help them 'forget' it to get some sleep - because they know that it will be there on paper when they wake up.  You could also try changing your night time routine.  For about 1 hour, or half an hour before going to bed, do the same thing every night - take a bath, read a book, drink something non caffeinated - the same routine in the same order, so that you are 'preparing' your brain to go to sleep.

Try some stress relief remedies too, if the stress is really bugging you -relaxation techniques, calming music, anything to help you unwind.