My two cents? If you go for a while eating very low calories, your body becomes accustomed to that and when you eat more, it "stores" the extra calories. There is some disagreement as to whether the "starvation mode" hypothesis is true or not, but I can say I have experienced it firsthand. I can go on 800-1000 calories a day and not lose anything, and when I up it to 1200-1300 a day, I start losing again. If your body gets used to low calories, it can treat anything above that as excess and hold onto it, regardless of your metabolism.
Looking at your goals, I am wondering if you are trying to lose too much too fast; it may be backfiring on you.
"If you drop an egg, you don't say, 'Oh, shoot' and drop the other 11, do you?"
-Source unknown, but obviously brilliant
Reached goal 4/16/2010...but kind of afraid to look these days