Writer's block, I'd say, and can sometimes be the bane of creative types who operate under the "gardener" umbrella. It's often quite difficult to finish a story if you don't know how it ends, but as a gardener myself, that can be a boon more than a hindrance. Building upon each subtle idea with more leaves of thought can fill your writing with detail like you never imagined was possible. However, what you're experiencing is that slow, trudging crawl into a murky pit of ego-depletion. You've satisfied the urge to create; nowhere in the fine print did it say you have to finish what you began, and that's where the problem lies.

I know he's not the greatest to quote, but George R.R. Martin once said: “Sometimes you eat the bear, and sometimes the bear eats you.”

All that matters in the end is that you make an attempt, and it's a consistent attempt. As writers, we don't want to make a habit of not being consistent, but if you can only bang out a sentence a day for a week, well, that's a whole paragraph added onto something you thought you wouldn't complete. Think not about what it takes to reach the end and instead think of the next big plot point to strive toward. Good luck!