Elisheva,
I used to write a chapter every month to two months. I didn't want to write something that wasn't correct and I wasn't sure on the plot at that time.
So an example of what I'm dealing with right now…
I'm stuck with the characters in a place where they can talk, have time, and at least one character is aware of something 'not quite right'. I have to get the conversation to make sense. In other words, it's time to pass out some clues. So I'm going to write the second half of the chapter and get that over with. I have that part in my head and it is action, so it should flow pretty easily.
Another way that I get my writing faster is to write future scenes that will tie in with the story later. If a battle or encounter is really strong in my imagination, I find that I replay that part of the story in my head. I have to write it out to move on. This is how I used to write all the time. The disadvantage is that you have to connect the dramatic parts with less-interesting moments that don't hold attention as much.
The contribution of this site to my writing is that it made me write/publish in sequence. Now that I see the value of linear story, my piecemeal storytelling can come out of the closet and get thrown back into play…it isn't a disadvantage any more. I just don't publish those chapter until they are linked into the linear storytelling.
So anyway, consider writing ahead of where you are in your book. It really helps you with the overall plot. Even better? Write the ending. Having a destination for your story is a HUGE mental leap. It gives you somewhere to aim your arrows instead of just writing onto a blank wall.