Guest...great you've got a publisher but that does create some pressure, I imagine. And pressure, alone, can precipitate writer's block.   Good advice to just write...anything...even if it's just pages of "I've got nothing to write about." If you do that long enough you WILL write other stuff as well.

The Artist's Way is a good general creative spur, but you also might try reading Writing Down the Bones, by Goldberg, Writing for Your Life, by Metzger, both very motivational and inspiring in non-blue sky ways; or even Overcoming Writing Block, by Mack and Skjei. The last is more simplistic but even obvious suggestions, like taking a prompt from ANY sentence taken at random from any source (the Bible can be a real challenge!), doing 100 word vignettes on people, objects, places, etc., taking a crack at turning already existing prose into poetry as a change of pace...all stuff just to jolly your writing mind into behaving itself.

I'm sure your Muse hasn't abandoned you completely. If you've got 5 chap. written, you can write 5 more. Good luck.