Hi Hercules,,,it could be many things, sorry can't tell by your username if your male or female,,,I'm guessing male (soz if wrong) it could be your body holding on for its life to its fat stores, as it might have seen you crash dieting before so its gone into starvation mode,,,9lbs in two weeks is still excellent, I know its disheartening but you've got to look a the bigger picture, next week you shold have a huge weight loss, and Cambridge say that it averages out at 14lbs a month, so I say stick with it and see what next week brings...
Good luck x x