Dilemma

When I eat carbs (fruit, whole grain bread, cereal, etc) I have awesome energy and awesome workouts. I can definitely go longer, farther, and harder. However, when I eat carbs, no matter how much I workout I cannot seem to drop weight. To perform at a higher level I truly believe I need to be lighter. Cut carbs and I am able to drop some weight. But my energy lags too. Whats a girl/triathlete/endurance junkie to do?