Having trouble losing weight

Patient: I am 5′ 4” and weigh 150 lbs. I have been using an elliptical machine for 20 minutes, three to five times a week as well as approx. 15 minutes of stretching since November 2012. I have not lost any weight and my clothing fits the same as it always has. I have cut out eating snacks throughout the day and eat only a reasonable breakfast (banana and a V8), lunch (sandwich) and dinner (varies). I don’t know what else I should be doing. ??