its unhealty to gain or loose more then 5 lbs a week at the very most atleast thats what docs have been telling me just be careful and keep yourself hydrated
It's generally considered safe to lose 1-2 pounds/week. How did you determine that you need to eat 1200 calories/day? And how do you know you are burning 300 calories/day?
The number of calories you need/day should be calculated, based on your current height, weight, age and activity level, rather than a random number. I doubt that 1200 calories is enough for you at this point, and eating too few calories can prevent weight loss.