What is causing this?

All of the sudden I am having the hardest time getting a good nights sleep. I keep waking up and then not being able to get back to sleep for a long time. I can’t figure out what might be causing this, so I was hoping someone might be able to point me to a few good websites on insomnia causes. Hopefully if I can figure out what the problem is I will be able to do something about it so I can get back to my regular sleeping schedule. I know I will feel a lot better if I can just get some sleep.