This happened to me and has been persisting for years!
It seemed the first time around, because I had so much more weight to lose and was so miserable at that time, that I didn't want to waste a single day that could help me move toward my goal.
Now that I'm at a lower weight than I ever thought I'd be, and 'content' (rather than 'happy') with my body, that drive just isn't there anymore, even though I still want to become fitter and leaner. I've become complacent.
It's a difficult rut to get out of, isn't it?

I'm not sure how well it is going to work, but right now my goal is to focus on goals that aren't necessarily "weight loss" goals. My desire to become a runner has helped me stick with an interval running program throughout the last month. I'm not sure I would still have the motivation to keep with it if my goal in mind was "lose more weight" rather than "become a runner", so I'm hoping these sorts of changes in thinking will help, and that weight loss will be a "side effect" of these other goals.