8 Factors That Could Be Keeping You Awake At Night

This is an interesting list which may help in finding a reason for your sleep problems.  The factors are: pain, mental illness and stress, snoring, jet lag (yes this can cause chronic insomnia), shift work, hormonal changes, medical illnesses, drugs.  Each of these is explained in more detail here when you click on each of the links:
http://www.health.com/health/gallery/thumbnails/0,,20306729,00.html