I've noticed with my own dieting that I have to watch my carb intake. Even when I'm down on calories below 1300/day, if carbs make up more than 50% of my calories, I'm going to either be up on the scale or stalled. Now the opposite is true if I get lots of protein. If I can keep the protein up to 25-30% then I can have as many as 1600-1700 calories and still be down the next day. And eggs goof up the whole works, if I eat them I can have 3-4 whole eggs in a day which skyrockets my fat percentage, but I will likely be down the next day provided my caloric intake doesn't go over 1700-1800 and I keep my carbs to less than 50%.
So in answer to your question, use the fitday tools to see where your calories are falling, give them a study and maybe that will shed some light on it. It also could be that you're building muscle, sneaky little devils. You might also increase your water intake, 8-8oz glasses/day + an additional 8oz for every 10 pounds you want to lose - ballpark. You also might need to add an additional amount of exercise to get past this plateau. Recently I had to increase my workout by 15 min/day just because my body had gotten used to the old routine. Keep in mind the calories you burn during a workout are based in part on your weight, so the lighter you are the more you have to work to get the same burn.