You've got to cook out of it lady, just having the book doesn't help!
I've still only tried one of the recipes, have you been eating mostly the stuff from the book or have you been mixing things a bit? I am not keen on the author's low calorie limit, if you are following this it may not be enough for you, sometimes you need to eat more food to lose weight (more good food fruit and veg etc).
I'm not following any diet, just making it up as I go along but I aim to drink 2 litres of water a day, eat at least five portions of fruit & veg, include about a 1/4 pint of skimmed milk into my day somehow (I don't like to drink milk so yoghurt or milk in tea or coffee) (apparently it boost metabolism), try not to drink fizzy drinks (they slow metabolism, ahem glass of diet coke at my side as I speak, for the sore throat honest), avoid things with too much cheese, deep fried etc, try to exercise three times a week and walk whenever possible rather than take the car or bus.
It seems very strange that you have not lost anything in three weeks though, you're not pregnant are you?????
I think there are a variety of diets going on here so I am sure we will be able to help you get off the starting blocks. Tell us about your diet/exercise and hopefully someone can help?