So, my sleep is just a little weird.?

So here's the thing, I used to have a problem where I could not get to sleep until 5 am. Didn't matter if I worked out, worked at my job, took sleeping pills, nothing really changed when I could go to sleep. Then one week was unfortunate enough to have two things scheduled at 8-9am. I woke up at those times, and took the opportunity to try to change my sleep to those times. Now I go to sleep more around midnight, trying to wake up at 8. The thing is when I go to sleep at midnight, I never sleep 8 hours like I used to. I get 5-7 unless I fall back asleep, in which case I oversleep. Anyone know why?