Why the Scale Lies.
Another post on the same topic, this one dealing more specifically with low-carb diets and how they affect water in the body.
Required reading for any frequent weigher!
Water makes up 60% of our body weight. Sodium levels, hormone changes (not just "women" hormones, but the ones that regulate our appetites and everything else), glycogen levels, etc. -- it all affects our weight. Plus, our "weight" on any given day is not just fat... but bones, muscles, organs, etc. When you lose a pound, the scale doesn't tell you whether you've lost a pound of fat, a pound of water, a pound of muscle... or some combination therof.
I'm not saying not to weigh yourself! I'm just saying that you need to be aware of what that scale is measuring, and the many things changes in that number can mean. What you need to focus on is the TREND in the numbers overall (and not just over a week, but over months).
And when you just can't deal with the scale any more, focus on your NSVs (non-scale victories), which can show so much more how your body is changing, shrinking, adjusting, than just a number on the scale. Are your clothes feeling bigger? Do you need to pull your belt in another notch? Are you finding it easier to walk up three flights of stairs? Did you ignore the break room doughnuts completely, until you were back at your desk, when "before" you would have obsessed over them? All of those are milestones along your journey just as much as a change in the scale is.