I got below prepregnancy weight after breastfeeding my son, very quickly as well, so keep it up, eat healthy, and exercise and you'll be just fine!
You do have to work at it, and breastfeeding can be pretty draining so there is always the temptation to stuff your face with whatever is available. My advice would be to make sure you only have healthy foods in the house & to drink a big glass of water everytime you feed!