Creativity, very much like love, is a gift. And you don’t get to get gifts all the time. If you go on a date and you don’t like the guy or girl you are meeting, you are not experiencing “lover’s block”—you simply don’t love at that moment, and if you’re patient enough you’ll experience love in the future (probably in the place and the time you’d least expect it). If you don’t write well, keep writing bad stuff (don’t worry, bad writing is completely ecological—it doesn’t damage the ozone layer or give you cancer). If it gets too frustrating, stop doing it—move on to badminton, collect airplane models, or do all those other things that people who don’t write do. But mostly, wait patiently. (Patiently as opposed to impatiently, or angrily, or bitterly—because those kinds of waiting don’t breed future good writing. Patience does.)
Writing isn’t a habit. It’s a unique form of expression. And nobody owes you that special experience on a daily or a weekly basis. But if you make an effort, when it’s gone, to keep living your life and experiencing new things, it will eventually return. And when it does, enjoy it as much as you can, before it goes away again.