I am a massive insomniac and have been since my first pregnany 9 years ago. I often am able to fall asleep, but cannot stay asleep. Here are a few things that have helped me:
The best thing I have found recently is something called Deep Sleep soft gels.
http://hono.stores.yahoo.net/hemedesl60.html
These take a few days to kick in, but are a life saver. I haven't taken them in a while, but realized tonight it is time to start again, as the insomnia is back.
Put a drop of lavender eo on each side of your pillow. One drop is enough (my mom drenched her pillow case when I told her this and couldn't sleep due to the smell!

)
Sleep hypnosis CDs (Hypnobabies has one, although I haven't tried it. I did fall asleep last night to a Hypnobabies CD, though). Sound machine/ocean/rain/storm/river etc CDs.
Take naps during the day to make up for the lack of sleep--sleep experts will tell you not to do this, but with only 5 hours over a few nights, you need to sleep some time. I find that if I nap, I can some times catch up.
My routine when I wake up is to go downstairs and engage my mind for a while with the computer (hence why I am posting at 4 am

) and simply acknowledge that I am awake. [My mom who was a pregnancy insomniac as well would just get up and do laundry and other stuff until she was tired again.] Then I turn on the TV to something mindless and go back to sleep. By mindless, I mean stupid, like the A-Team, which always seems to be on when I am up in the middle of the night. If I put on something new or interesting, I can tend to get wrapped up in it and not fall asleep.
Read a technical book. I am in the retail business, and I have these merchandising books that can be so boring, they knock me out. When I pick up Stephen King while having insomnia, I am up all night. An older book, in older English, that requires focus to read, works for me as well. I had a book of horror stories from the early 1900s with Poe and other writers that didn't flow easily due to the language differences, and it knocked me out.
Call your midwife/doc and find out what ideas they have as well. I have gone into one labor totally exhusted after not sleeping all night, then going to work the next day, and finally going into labor at 10 pm. It was horrible. I couldn't mentally deal with the labor, couldn't remember what I had learned in birth class, and ended up with an epidural, suction cup and forcepts birth. If I had had some rest, I think the birth might have gone a little smoother.
Good luck! I so totally understand where you are coming from.
