The first week (or two weeks) you lose mainly water weight and generally there seems to be a correlation between those who have a lot of weight to lose finding that they hold a lot of water, so the losses in the first week or two tend to be more than those who don't have as much weight to lose overall. However in your case, if your stats are correct, then it doesn't look like you have a lot of weight to lose so you should be really pleased with this result - it seems your body has taken really well to the diet and hopefully it has already got rid of all the excess water and moved on to fat already. Don't be concerned, be happy!