I am not sure why you need to lose weight so fast; however, you may want to increase the amount of water you drink and try the Atkins Diet. This is ok to follow short term in an effort to kick start your diet. Fat weight loss is not healthy and often, you will gain back the weight quickly.
Remember, exercise reduces fat and builds muscle. There is a theory that muscle, weighs more than fat.
Here is the Atkins Diet website:
http://www.atkins.com/
A group of nurses (including myself) swear by the South Beach Diet, we all lost between 4 and 8 pounds the first week. It is the only diet that I and some of my friends have been able to stick on, lose weight and maintain our weight.
http://www.southbeachdiet.com/index3.asp