I didn't lose this week either.
It happens from time to time. I actually believe it is just water--and the effects of being horribly inconsistent with my exercise.
Look back carefully, see if there's anything you can do. How much exercise are you doing? I'm not asking in order to tell you to do more, not at all. Sometimes doing too much can stress the body and make it retain water. (or so I've read.)
my weight loss blog: http://mypsychemysoma.blogspot.com/
"Your best weight is whatever weight you reach, when you're living the healthiest life you actually enjoy." Yoni Freedhoff