… it’s probably time to pick up a book and start reading.
It doesn’t matter what book. It doesn’t have to qualify as great literature. Even if it turns out to be total crap, you’ve started to think about what makes it total. Where are the holes in this argument? Why are these characters so flat? How could it be improved. Once you’ve started thinking through that, you’re on your way to thinking through what got you stuck in the first place.
And, if it turns out that you did happen to pick up a masterpiece, you’ve just opened your mind and imagination to a whole new dimension, and now you can go places you didn’t even know existed before.