On a perpetual diet, but can't lose weight. help?

I have been on a perpetual diet for like 6 months. I don't understand why I can't shed a pound. I eat about 1200 calories a day, and work out for about 30 minutes a day at least. I get nowhere. Does anyone have suggestions? I'm desperate. I don't want to go on a crash diet, but I have a feeling that I am pretty soon going to try the 800 calorie thing.