On 1200 calorie diet (prior to diet 2000 a day)for a week drinking only water, eating healthy and exercise 4 days a week, i have lost 0 pounds, why!?

Keep it up: In general one gains weight when one consumes more calories than they use up during the day and lose weight if they consume less. If one exercises as stated, they probably have more solid mass than fat and it takes a little longer to notice on the scale. it is also possible the calorie count may be inaccurate. That said this 32y/o female is doing well. Keep it up. It will yield in due time.