I am prone to weight gain in a week i can gain up to 9 pounds i have to b very strict to b thin y?

Reduce weight: That may be the case. However, you should see your doctor to make sure your thyroid and other hormone levels are all normal as this may contribute to your weight gain. For eating, try making small changes. Eat the right portions, eat 3-5 small meals a day, cut back on carbs and sugars, increase lean protein/veggie/fruit/water intake, and start doing some cardiovascular exercise.