I pump and give breastmilk during the day. At night, we give her formula. How do I know if my breast milk is 'good'? When it's in the fridge, the layer of fat is not very much. I admit that I don't pump as much as I should. Our baby is two weeks old. She seems to prefer formula. She is always spitting up the breastmilk (even though I give it to her when she's hungry). She doesn't spit up the formula.