How old is your baby? I hear, once your body is used to breast feeding your body produces milk when your baby latches whereas in the beginning your horomones are what make the milk.

Kalli is now 13 months old and it doesn't feel like there is milk in there at all but once she latches and my let down comes in I can hear her gulping and watch her swallow.  Make sure you see these signs before you start adding formula (if you still want to BF), the less you bf the less milk your body will start producing because your body will assume your baby is skipping that particular mealtime.  Keep that in mind.

Maybe try nursing first and then topping up with formula.  If your baby is still a newborn the more formula you introduce the less milk your body will supply.

Good luck.

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