Aww, Kelly, I'm sorry you're feeling this way. Like everyone else has said, I think a slump is something every writer goes through. There seems to be a pattern with this:
When you first start writing, it's all fresh and new and fun, and you have SO many ideas, that it's easy to just churn out chapter after chapter, story after story, and update all the time. I know the first year I wrote fanfic, it was rare to have a day where I didn't have an update on my site. I posted at least one chapter pretty much EVERY DAY, and as soon as I finished one story, I launched right into another.
After awhile, you start to slow down. There are lots of reasons for this: real life gets in the way and cuts down on your writing time, you have written so many things that new and original ideas are harder to come by, and as you get better with experience, you also get more critical of your writing, so it takes you longer to finish a chapter you're happy with. At least that's how it was with me. After a year or two of writing, I slowed down. I updated maybe every few days instead of every day. Then once a week or so.
And then, for me, real life happened. College... and then student teaching... and then teaching for real. I had other things going on and other things to think about, and even when I would sit down with some free time to write, I would think about all the other things I felt like I should have been doing. Homework, lesson plans, grading papers, job searching, apartment hunting, all that good stuff. It really just killed my inspiration. This past year, I kinda gave up on even writing much on weekends and just looked forward to actual breaks - Thanksgiving, Christmas, spring break, and now summer - to do some major writing, because weekends were my time to relax and get caught up on other things.
So it could be that real life is interfering, whether you realize it or not. You can think to yourself, "I have two hours of free time right now. That's plenty of time to get a couple of pages written, so why aren't I writing?" But it's not that easy. Maybe it used to be easy, when you were churning out update after update, but it's not anymore. You have to get in the right mindset, put everything else in real life in the back of your mind and focus on your story, and get that inspiration going, and that takes some time. If you're worrying about all the other things you have to do, or worrying that if you DON'T get an update out, you're going to disappoint people, then you're putting so much pressure on yourself that of course you're not gonna be able to write anything.
I think the pressure is another major factor. If you used to update all the time, and your readers expect that, and now you don't update that much anymore, you feel like you're letting people down, and then you're putting a lot of pressure on yourself to get updates out quickly. And like Mare said, that takes the fun out of it. It makes writing feel more like homework, when it should be just a hobby, something to do for fun. You just need to relax and not push yourself. So what if you only update once a month or less? The readers who truly enjoy your story will look forward to your chapters that much more. They may not enjoy waiting, but they will wait for you. And they'll understand, especially those of them who write. We all know how it is.
So my advice is:
1) Don't worry about it because it happens to all of us.
and
2) Relax, take your time, and don't pressure yourself to update. If you pressure yourself, you'll just make the slump worse because you'll take all the enjoyment out of writing and make it feel like a chore. If you're stuck or just not feeling it, then take a break and wait for the inspiration or feelings of withdrawal to strike. It might take some time, but eventually, there will come a time when you'll get bored and feel sort of an emptiness and think "I should write..." Maybe then the love will come back.
Sorry, that was a REALLY long post, and I have more to say, but I will save that for another LOL.