This is my problem most of the time.

Writing comes pretty natural to me. If I have writer's block, I just remember what inspired me in the first place, and I try to get that feeling back.

If you don't know what to put in the middle, then re-watch or re-read whatever it is you're writing for. Pay attention to the small details, because behind every detail there can be a storyline.

I have to work on my spelling and grammar, because English is not my native tongue, but I don't feel like it's a constant battle.

I make time to construct it. It's freaking past 1am, I'm getting cramps in my hand, but my notebook's right beside, and I've already written a page and a half of chapter 17 of Foster Careless.

If I have to name something, I would say that I sometimes don't know how to start a chapter, but once I do, I usually don't know how to stop, lol.

@HaleyDewit: Thanks for the advice! That helps. :) As far as your last comment, I can be the same way sometimes. Once I figure out where to go, getting there usually isn't a problem. :)

Writer's block or losing inspiration. Occasionally the middle stuff.

If I can't name something currently, I'll sometimes wait to post it or start it off unnamed. But I don't add mine to FF (they're more original stories than fanfics), so I don't know if it's a possibility there.

Lack of free time to do it.

Or having certain ideas/scenes planned, but needing to come up with filler ideas to pad up other parts of the story.