Question: What do you do when your writing in not flowing?
Many times when I cannot write, I move to editing something I've already written. If you're like me, you always have something that needs editing. When I'm not editing, I like to journal in a stream-of-consciousness or give myself permission to write something about the backstory of my characters. I'll write a scene between a mother and her daughter that took place years before that will never appear in the story, but will inform my understanding of the characters. The scene can suck. It can be about whatever because no one will ever read it, but it moves me deeper (not necessarily forward) in the writing process.
If it's an option (i.e. the deadline is months away) I will not write. I'll go play tennis, read a comic book, spend time with my wife, or watch a television show. That violates the question a bit, but that "break" is often the thing that dislodges the food that's clogging my drain (brain). Repetitive motions are also good. Bouncing a ball off a wall like an inmate in prison can help you break free.