How do I know how much milk to give at each feeding?

wilburbud

I'm going back to work in 3 weeks, and I've bee pumping and giving Dd a bottle once a day to keep her comfortable with a bottle. Some times she will chug down 3.4 oz- other times just 2. Whenever she eats a lot, like 4 oz, she throws up. I've tried feeding her just 2- and she throws a fit wanting more. So how do I know how much to feed?