Hey Cindy,
Ok, realizing that you were given a diet by a nutrition center, I'm gonna say something that's maybe not intuitive. It's up to you whether you want to consider deviating from what they gave you.
At your weight and height, 1200 calories is NOT ENOUGH FOOD.
1200 calories is the minimum you should be eating unless you're on a medically supervised program and taking supplements for nutrition. If you check out most calorie calculators, they'll tell you that you should probably could consume 2500 calories a day to maintain, and 2000 calories to lose. (Actually I put your stats into this calorie counter and came up with a figure of 1976 calories to lose:
http://www.freedieting.com/tools/calorie_calculator.htm)
I started out at a little less than your weight - 237 (actually, to be truthful, I didn't weigh myself for the first time until after I'd already started losing, so I suspect I was well above 240 when I started) and I ate 1800 calories a day and lost steadily.
Here's the thing - your body NEEDS nutrition to maintain a level of metabolism. If you slow your metabolism by drastically cutting your calories, then your body goes into what a lot of people call "starvation mode" - in other words your body freaks out that something is terribly wrong becuase you've gone from eating a lot to nearly nothing, and so instead of losing, your body tries to hold on to everything you've got.
It really does make sense, even though it seems counter intuitive at first.
I dont' want to recommend that you go against anything your nutritionist has said, BUT ... if it were me ... I would try raising my calories to 1600-1800, making sure to get plenty of protein, and continuing with the exercise program you've described.
I suspect your body will kick back into gear as soon as it starts getting enough nutrition.
.