overweight help??

I am like 140 pounds, on a 5' frame. i know i am overweight, and my docter has told me the same thing over and over, "eat less/healther and exercise more" well i eat fruit for breakfast, a light lunch(or nothing if i'm not hungry) and a healthy dinnner.... and I've GAINED WEIGHT!!!!!! also, i exercise twice a day, and do crunches whenever i have spare time... CAN SOMEONE PLZ HELP?????