I'm afraid, Lil, that you're just one of those people that can't get less than 6 hours of sleep. Most people, in fact, are zombies when they get less than 6 hours of sleep, despite the fact that too many get so little frequently. Personally, anything less than 8 hours is going to cause me to have a bad day, and I prefer to get 9. I used to rack up 10-11 hours on the weekends, but now that I don't have room-darkening shades on the windows, the sunlight gets me up naturally before then. People have been asking me since high school how can I get so much sleep; they just have so much to do before bed! I look at them in equal confusion and ask how they can't stop what they're doing and go to bed? BED is all powerful, BED is all-fixing, BED is just ALL. Sometimes, on the weekends, I just get in the bed and roll around and waller in it for a few minutes just to commune, then go on about my business. Sleep is not that annoying thing we have to do when we could be doing other things (although I do view bathing as such--I can't wait until they invent a waterless sonic shower that just pulsates germs, oil and dirt off you in under 30 seconds, but I digress).
My bedtime is pretty well set. I get sleepy between 8 and 8:30. I almost always lay down in bed and read a little bit before going to sleep. Even if I don't feel sleepy, if I have to work the next day, I will get in the bed by 8:30 and lay there reading until I get sleepy. I will eventually get tired enough to sleep. Luckily for me, I've always slept like a log. I only have trouble sleeping when I'm sick or I'm alone (haven't gotten used being alone in the new place--despite Stuart being out of the county for almost three months earlier this year). I may have a true bout of insomnia once a year.
If you have trouble sleeping, you should see a doctor. Light therapy in the wintertime can actually help you sleep because it helps regulate your body clock, so you can go to sleep when you should. Avoid exercising more than a couple of hours before going to bed. You may want to eat more than two hours before going to bed if your stomach is likely to bother you, but I find I can go to sleep regardless--although laying down with a too full stomach isn't very comfortable at first. Spend the last hour before bed winding down; check your e-mail, read the paper, watch t.v., read. Turn off most lights or dim them where you are doing your winding down because that will help tell your brain that it's getting close to sleeptime. Don't be cleaning house and wrestling kids less than an hour before bedtime or you'll require more time to wind down and de-stress.
My fiance sleeps pretty good most of the time, but he will go through periods of insomnia fairly randomly. When he has one of those nights--he will fall asleep, but wake up within a few hours and have to get up and do something--we can expect him to have more of them, so I always remind him to have a sleeping pill before going to bed the next night. That usually keeps him asleep and breaks the cycle (although he may take a sleeping pill the second night afterwards as well). Without them, he can have insomnia for a week or more.
I'm afraid I don't know of anything to correct a lack of sleep during the daytime short of a nap or coming home and going to bed early. The best medicine in this case, I think, is preventitive.