Keeping speed and motivation up

Currently I am working on the second book of a YA series. Things are moving forward, mostly due to a good pre-structuring. But still, progress could be better. I managed to sit down with my laptop for about two hours to work on the book, however having spent the most of two month on the first third of the story, it is still a long way to go. And due to traveling, I have less time at hand. During the week in a hotel room, it is not so much about motivation but about sheer tiredness (when I am on the road, I usually get up around 6:00 for my morning run and rarely return after dinner before 22:00. And the last two hours of the day are mostly spent unwinding.