I think it's because you haven't got that much to lose. Those with alot to lose tend to have bigger losses. It could also be due to the fact that your body is in shock because of the lack of food and is adjusting to the diet.
Anyway, I think it's still a good loss. Better to lose a little than gain I say.
My losses are awful at the moment, I am only weighing in every two weeks now with my CDC but on my scales I am not losing at all at the moment, funny thing is I am stuck at exactly the same point as I was a few weeks ago but this time a stone lighter, I literally spent a week at 12stone 6lbs with no movement and now I am around the 11stone 6lbs mark and it is not moving again !