Some weeks you really can't force out creative/productive work. That's why, when I'm feeling good and inspired, I try to churn out as much prep as possible for my #DnD game prep.

Some days you'll just be more productive than others, and that's okay. Don't force yourself to be creative - just go work on something else. Follow your muse and do those "unproductive" side notes, sketches, headcanon blurbs, whatever you need.