I had that problem too, when I was in college. I'd stay out all night partying, and I didn't have classes until 10 AM or so. Then I graduated and had to start getting up at 6:15 am every morning for work. At first, it was really really hard. I overslept and nearly got written up a couple of times. Once, I was an hour and a half late!! Eventually, I started just getting tired earlier. Now if I'm not in bed by 11:30 pm, I fall asleep on the couch. I understand now why my parents always did that!!!

I think in time, once you go back to school, it will work itself out. Also, working out during the day can help make you tired at night. So can laying out (sun zaps energy). If I'm desperate, I take a super-hot bath, dry my hair, and immediately get back in bed. Usually works for me!

Good luck!