You can't lose four pounds of fat in four days unless you are a super athlete. Losing a pound of fat requires burning 3500 more calories than you consume.

Your weight is probably fluctuating because a lot of the changes in your weight are simply changes in the amount of water you are holding. I try to focus on the long-term trend and not the day-to-day fluctuations. My weight fluctuates 2 or 3 pounds up and down all the time.