When I got to chapter 7 of my series, I was already facing writer's block! Some authors have said they don't even use an outline; just that they know how it'll end and they make up the rest when they get to it.
I stopped writing and it took me 3 weeks to finally make an outline of where I wanted to go from the beginning, middle, and end. I'm still toying with the transitioning stuff, problems they'll be facing at the beginning and their solutions at the end, items that will make sense later, etc.
If you're just going along with it, I don't know how you guys do it.