I think we're hitting this now too.
A lot of it is teeth related. In the last couple of weeks his top canines have come down into position, although they're not through yet. And not only that I'm still waiting on his last molar (1st set) and a 4th bottom tooth that has yet to appear!
While the canines were moving around it was soooo hard to get him to sleep. I'd be outside his door listening. I cold hear he was trying so hard to get to sleep but then he'd just cry out in pain. Bless him he was so good through it though, even though it was taking 30-45 mins for him to finally drop off. I'd only go in if his crying became prolonged and he needed a bit of reassurance.
So anyway that's stopped now, he's going to bed fine. But in the last few nights he's been waking at various times, 1am, 3am, Sat night it was only 10pm! And I have to confess I've just been bringing him in with us as he's not settling at all, wont lie down, just sits up and screams and reached out for me. I do try but can't for too long as it wakes his brother up and then I have him to deal with as well. Big brother is playing up now too, but that's a whole other story, he's 5 and knows better!
None of us are getting much sleep at the moment!