I'm going to just direct everybody with questions like this to Andoreth's great thread about
A week in the life of a daily weigher.
There are 100 reasons why the scale might fluctuate. For me, it was important to look at trends over time and not get hung up on daily numbers. For awhile, the scale had a very unhealthy influence over me. If my weight was down, I was positive, motiviated, ecstatic and convinced I COULD DO IT. If the scale was up, I was depressed, de-moralized, felt like all my hard work was wasted and I would never lose weight. Because I could never get the hang of accepting daily (heck, HOURLY) fluctuations, I eventually had to force myself to only weigh weekly. Same time, same method every week. That really gave me the consistency I needed to stay motivated and on track.
Sometimes, no matter how "good" I was - how much I exercised, how cleanly I ate, the scale didn't move at all, sometimes for a few weeks at a time. This is really tough, how does someone stay motivated when they aren't getting that positive reinforcement from the scale? The closer I got to my goal weight, the more common the "plateaus" became, culminating in a 12 week plateau that was really really hard for me.
For that reason, I think it's very important to make reasonable goals that aren't related to the scale at all, but are more in tune with lifelong health. If you eat 5 different vegetables a day, workout 3 days a week and go to bed on time 4 nights a week, you may not lose weight THAT week, but ultimately you are making changes that will make you healthier. If the scale doesn't go down, at least you can say "I did something good for my body this week."
Make goals that aren't related to the scale (trying 1 new healthy recipe once a week or some exotic fruit you've only heard about) and then reward yourself for accomplishing your goal.