My fave hormone is CCK (too late at night for me to spell it) but it makes you feel sleepy when the baby feeds - you are meant to relax and go to sleep with your baby on your breast. Thats why research shows that breastfeeding mothers actually get more sleep than bottle feeding mothers (This is a FACT) even though the baby feeds more often - because the hormones of breastfeeding help them relax and get back to sleep quickly.
So your body is doing its thing perfectly!