I gained about 2 kgs in ONE day! :S?

Any time you weigh yourself after eating or drinking it will be more! You need to weigh yourself once a day at the same time each day, and no more. How much weight you actually gained depends upon how many calories you consumed, and nothing more. If you ate 3500 calories, that equals a pound. Learn your BMR (basal metabolic rate) which is how many calories you need each day to remain even. Then add or deduct each day depending upon if you consume more or less calories than your BMR. Nubers don't lie.. good luck