The type of carbs matters. I wonder how much of the carb demonization here is really code for high-glycemic stuff like cereals and bread, in particular sugary American bread.

If the carbs you eat in the morning are slow carbs, then there's no reason you shouldn't have high energy all through the day.

The other possible explanation is that you are young, and your body is (for a while yet) very good at regulating blood sugar.