Its funny how this weight loss goes. I have a friend who weighs more than I do, who started a week before me, and has lost 2lbs more than I have so far.
Think its a lot to do with your metabolic rate (get me, lol) and like you said, you might not have had as much water to lose.
Are you drinking enough water? That seems to really affect how much I lose, if I don't drink enough, the weight loss is slower. Just make sure you don't have more than 4 litres a day! It can be dangerous, plus you'd never get off the loo!