Hi everyone, I am new with a 10 week old girl. ...

Hi everyone, I am new with a 10 week old girl. She is on formula as lost weight b/f and appears to be lactose intolerant so ison soy. My question, it says that she should be having 6 feeds of 150mls each day on tin (other brand says 180 - go figure) but I struggle to get 80mls in her. What did other babies do and should I be concerned. ps, she has been constipated since on formula.