Exercise 2 hours, Eating 1200 calories Not Losing Why?

I weigh 188 pounds. I am trying to to get to 145lbs steadily over the next few months. I am eating 1200 calories of variety foods and im exercising 2 plus hours a day, cardio only. Am I exercising too much? Is is possible to do too much cardio? Im trying to lose 3-5 pounds a week. Any suggestions?