Writer's block is an interesting thing. A friend of mine insists it does not actually exist, and sometimes I agree. But I think there is such a thing as writer's fatigue. It's when you feel like you can't come up with what's going to happen next, or you are just tired of writing. Everyone has probably experienced writer's fatigue/block at least once in their lifetime. So here are a few ways you can combat this so that you can start writing fresh.
Take a break. This is a pretty simple solution. I don't mean don't look at your writing for three months, I mean separate yourself from the computer. Stop staring at the screen, and relax a little bit. Watch a movie, read a book. Come back and you might have a fresh view.
Do something active. Taking a walk, or riding your bike can clear your head up. You may even find yourself inspired in the fresh air.
Remember. Think back to when the idea sprung, or when you were so excited to get started. What was it? Did a character jump out at you in vibrant life? Did a plot come from nowhere? Think about why you are writing the story, and find that again.
Talk it out. It is extremely helpful to talk to another writer about your frustrations. Or to work out a plot point that is stumping you. This method has been helpful to me many times. If you're a teen, check Go Teen Writers for other writers your age. I've found many friends through the Facebook group, who are great to rant at... or rather talk out the plot with.
Work on another story. Having more than one project can be a good thing. If you need a break from a story, working on another project can help get you motivated again.
Read other people's work. I'm not talking about published authors. I'm talking writers who aren't there yet. Read your friend's book you were supposed to critique three weeks ago, or look up some stories you might like on a fanfiction website. Whenever I read someone else's work, it makes me want to write.
Push through. Sometimes you're in the dry spot between the two rivers of words. If you can just climb past the dry land, you'll find yourself in the words again. If that makes sense. If you push through the tough parts, you'll probably find yourself in a part of the story you enjoy writing more. And you can always go fix those dry areas later during revision. Things that help with writing through the dry spots are Word Wars/sprints. You can find them on Twitter sometimes, on the GTW group on Facebook, on a Word Wars group on Facebook, or you can just get with someone else, choose a certain amount of time to write, and see who writes the most words. Incredibly helpful. There is also a website called Write or Die where you have to keep writing, or there are consequences. That will sure make the brain work!
Keep writing. Whatever you do, don't stop. If you're taking a break, fine. But remember to come back. Your story calls. It needs to be written. Because no one can write this story like you can. You are a unique individual with a unique take. And your story needs to be told.