I think it's been determined that the lost weight was mostly water.
Since a pound equals 3500 calories, losing 4 pounds of fat in 3 days would be a pretty tall order. It must be noted that a 16 yr is not fully developed, and must be careful not to cut calories too much.
A lot depends on your weight when you start the diet. If you are 25 lbs. or more overweight then chances are 4 pounds in the first 2 days isn't unhealthy since it's probably 95% water that you're losing
Lose Body Fat
Have you figured out your actual calorie needs? If not, you might have cut too much. The more we weigh, the more calories we need to exist. We have to cut down slowly. Picking an arbitrary calorie count, usually, doesn't work.
You have to calculate your actual calorie needs (what you need to stay alive), then figure out how to create a calorie deficit -- either by eating less or exercising more - preferably both...
Thank you for your help I have been eating about 1250 cals a day so I haven't cut down that much and in regards to exercise well I haven't been doing much to be honest with you so you might be on the right track saying that is may be water weight so thank you for all of your help
Safe weight loss is 1-2 pounds/week. If you've lost 4 pounds in 2 days, either you've cut your calories, too drastically, or you've lost a lot of fluid.
How many calories are you eating, daily? Are you doing any exercise, along with the calorie counting?