Negative Calories (Breastfeeding and Workouts)

I have a question about entering breast-feeding calories. I read the forums and have been entering an approximate negative calories consumed based on how often my child nurses. I don't see any change in the daily calorie requirements based on what I enter.

I also set my activity level so that I would be working to stay under my calorie goal regardless of what workouts I do. So the negative calories from the workouts I enter don't count in my mind.

Today I finally checked out the weekly calories/nutrition chart. According to this chart, some days I was going as low as 600 cal. I am wondering if you don't see negative calories in any other view besides this one. I'm assuming the weekly calorie deficit is not really accurate since I am eating for my activity level rather than individual workouts. Am I reading this correctly? Thank you in advance!