I know what you mean, my body clock has always been wang eyed and I can't stay in a routine. Since new year and up until about a week ago, I was going to sleep between 4-8pm, which was quite surprising as my body clock doesn't stay in a routine for that long usually. Now I'm back to going to sleep between 12-4am. I'll probably switch to another time in the near future seeing as half term is coming up. But I can live with a dodgey body clock just fine.
How much sleep do you normally get a night and how much do you need so that you feel fine and not drained in any way?
You could just stay up all night one night and through the following day to whatever time you used to sleep at? Just a suggestion, helps me get out of a routine sometimes, temporarily.