I always get accused of being anorexic (which couldn't be further from the truth). I'm just skinny... I can't help it really. I certainly don't watch what I eat... I eat when I'm hungry and I stop eating when I'm not hungry anymore.
I'm 6ft and my weight hasn't fluctuated more than 3lbs to 5lbs since I've been this height. Currently I weigh about 120 lbs, and I just can't help it, it's genetic. I have a friend who is 5'6 or so and she weighs about 140lbs, she works out every day and diets all the time, she just can't seem to get much smaller than that.