I definitely feel the same way with motivation. I’ve gotten into the habit of treating writing like work, and on workdays, during work hours, I write, regardless. Sometimes I write fanfiction of my own characters doing silly things, or get unusual couples into steamy settings to see what happens, while other times I close my eyes and just try to describe every detail of the room I want my next scene to be in. I like to keep a sketchpad on hand too so I can make simple drawings. None of which actually contributes to the book itself, but you get the uncorking feeling of having done SOMETHING, and you can learn things about your characters you otherwise might have never discovered 0.o
When it comes to editing, I used to drag my feet too, until I heard this simple piece of advice – writing is the hard part, the world building. Writing is you, as god, standing in the whiteness and creating a world. Editing? That’s when you get to dive back into this pre-made snadbox where all the hard work has been done, and just fiddle around with it to your hearts content. The one book I’ve edited with that attitude ended up coming out so much better than anything else I’ve done.