I usually try to discourage any kind of cleansing while a woman is pregnant or nursing. Simply because when your body goes through the process of a cleanse there are toxins let out to the blood stream/breast milk. While many times the toxins are minute, there just is no way to tell if baby is getting those toxins or how much.
How many times a day are you nursing?
The other thing you would have to watch for is the ingredients you use in your cleanse and how they may affect your breast milk or baby.