The Institute of Medicine recommends eating 500 extra calories everyday while breastfeeding an infant.  To produce about 25 ounces of milk, it costs the nursing mother about 650 calories above her usual requirements.  Besides eating the extra calories from food, the remaining 150 calories are drawn from fat stores accumulated during pregnancy.  Calorie Count makes the adjustment, not in the Activity section, but in your Nutrition Analysis.  When selecting your customized diet for analysis under the "My Account" tab -> "Analysis", choose the option for "Lactation Diet".