Eleasha,
Maybe instead of looking for amount of writing completed, you should just make a habit of time spent writing. Start with a set time, for a set amount of time. For instance, I always write from 7:30 to 8:30 every morning. If I get more in than that, great, but I just make sure that that hour is mine, everyday. Even if what I write doesn't feel fully formed or fully productive I keep writing. I don't worry if one day I get 200 words because I know on another day I'll get 1000. Some days you click, some days you don't click so well, but that's okay. Allow yourself to have off days.
Another good piece of advice I found is (from Hemmingway I believe, but I'm not certain) to end your writing time on an upnote. In other words, when you have a some writing that is working well and moving nicely, quit while you feel that momentum is still going instead of writing till you feel you've spent all your energy. The theory is that if you finish feeling good about what you wrote then you'll look forward to coming back the next day and hitting the pages again. I'm not saying quit after five minutes because you wrote a nice sentence. I mean, if your set writing time is drawing to a close and you feel like you have accomplished a lot, feel free to put the pen down and keep the next scene in mind for the next day.
Good luck,
Sean