I'm afraid I cannot help you much about writer's block and motivation, because it's been almost 2 years since my PhD grant ended and I still haven't written half of my thesis... I feel like I'm in a relationship where there is no passion anymore but I'm too afraid to break up.

Don't thank me for cheering you up!

While it is reasonable to assume that you'll never get in trouble for copying one of your papers into your PhD, you really should check with your PhD's future publisher, because they might get in trouble.

Also check the RoMEO status of your publishers to learn about their policies: http://www.sherpa.ac.uk/romeo.php