Hi Sarah, First thing I'd like to say is "Poor You!" Joking aside though, it could be that your son has an illness brewing. I have found with my two (11 and 3) that they always get up early when they are sickening for something, especially the younger one who can start getting up ridiculously early for at least a couple of weeks before the illness comes out!
Ruling this out, it could just be a phase, which will correct itself.
Ruling that out, I would make a concerted effort to 'keep him going' all day, not to let him fall asleep or even be 'dreamy' if he is watching CBBC!
If that makes no difference, it could be that he needs to go to bed later as his body is adjusting. Bear in mind as well, that the damn hour has gone back and even this slight adjustment in time can throw out a child's cycle! In the summer, when the clock goes forward, it makes no odds but when it goes back it can wreak havoc!
I tried many ways to make my youngest sleep longer and I found that he only needs 10 hours sleep, whereas my oldest always needed 12 hours!
I hope my answer is helpful - I know how awful it is to wake up so early and I do feel for you - Let's hope it passes soon!
K