It'll probably help to do something else for a while, like you say. Arkillian's suggestion of short stories isn't a bad one, but if that seems too daunting then just making little notes to yourself, inventing a character and giving them a backstory for half an hour, creating a plot for a silly little story that's just playful and that you're not actually judging yourself on - I find those can all sort of let you be creative without the pressure of "I must finish this!" And once you have your "creative juices" flowing (what an odd phrase, but I guess it fits) then you might come back to your old story with a fresh mindset.
And sometimes just doing something else can help. Browsing the internet for inspiration is something I probably do too often, but it can yield new ideas. So can going outside and doing something completely unrelated, or working on a totally different problem - maybe a more technical problem which is more about finding a workmanlike solution to a problem and less about thinking creatively.