Every damn night...

My body is messed up. It's literally impossible for me to go to sleep at the 'normal' time unless I've stayed up completely the night before. Usually I only get tired at around 4-5am... Which really screws up my day. When I do get tired, I sleep the usual 8-12 hours, it's just that it doesn't happen at the correct time. Like right now. It's 4:40am on a Friday morning and I've been laying in bed in complete silence and blackness for 3 hours. Still couldn't get to sleep (finally just gave up and grabbed my ipad). So now I've got to stay up all day feeling like complete crap while trying to write an assignment for uni. I hate it. I hate it. I hate it. Any tips for getting tired earlier? Does this happen to you?