First of all, let me say that my younger son nursed until he was almost 3. There was a point there I didn't like to sit down because every time I did he took a nursing break! It was usually just for a minute or two, but at the time I was convinced he would go to high school nursing.
I just gradually started setting gentle limits and nursing times. Instead of saying "no" outright, I would say, "Let's wait until just before naptime and then we can cuddle for a while." Then we just had nursing times upon waking in the morning, at naptime, and at bedtime. Gradually, we got down to only the bedtime nursing. (It helped to have Dad go in the morning to get him up rather than me. He forgot about the morning nursing after a while.)
As to how you feel.....newborn nursing, where nursing is supplying all of a babies' needs....'costs' about 500 extra calories a day. This diminishes significantly when the baby starts eating real foods, but still, as long as you are producing milk, you have higher calorie needs.
I don't know enough to tell you about carbs and breastfeeding, but I can suggest that you make sure you eating enough high quality fat for your energy needs.