You know when you've been sluggish, swoon-y and vomit-y for what feels like your entire life, then when you finally go to the doctor and test positive for mono, you go, "Ah, jeez. Mono? This is gonna suck!"
Then the doctor gives you a dopey smile and says, "Well, at least we know what's wrong now."
Yeah, I guess we do, doc.
I recently went through the writer's equivalent. (Although unlike mono, most of us experience it more than once in our lives.)
I spent almost three weeks dragging myself through one scene. Part of it was because the workload for my course is more intense than anticipated, but mostly it was because the whole time I couldn't shake this feeling that something about the scene was wrong wrong wrong.
Good News: I found out what was wrong. I was in the wrong character's head the whole time.
Bad News: The characters are way too different for me to just swap the pronouns and call it good. I now have to rewrite the whole thing.
More Good News: The words will probably come a lot more easily this time.