I really had to slog through my Master's thesis. I think in part because it was my first time really writing an honest-to-goodness paper. It isn't easy to get yourself going, which I still struggle with today (as do many writers of all creeds). I think what got me through it was focusing only on what I had to do next. Looking at the big picture is nice for when you need the big picture, but it is terrifying when you realize how much has to get done. A "to do" list helps, but I wouldn't overload it with stuff because that makes it seem daunting. Rather, note what you absolutely have to get done next, as well as the few things after that. Writing the thesis is a matter of doing and nothing more. You've done all the brainstorming, you've got the goal set, now it is time to crunch right through it. And that begins with the first step.
As an example, whenever I didn't much feel like writing but I knew I had to start or it would never happen, that is when I would sit down and write the first sentence, however lousy it might be. Then I would try for the second sentence, etc. It seems like a no-brainer, since that is how most things are written: one sentence after the other. But it is easy to get distracted by, well anything, and you may hav eto make yourself focus on each little individual step for a while. Once you get going, it can turn into real progress very quickly. I still follow this plan of attack to this day when I need to write or get something done that I am not very inclined towards doing. Often I begin with an outline because it is like a to do list in its own way, then I work up to the first thing i need to write, etc.
It is simply and boring advice but, for me at least, it works.
Oh, and by the way, once I got through the thesis, the dissertation was a breeze. There's nothing like realizing you can get it done to motivate you to get the next thing done. In summary, you can do eeeeet!