I have been using a nipple shield to breastfeed my infant (she was born at 36 weeks and is nine days old). I am concerned about my milk production. How much should I be pumping after each feeding? I'm also concerned that she's not getting enough milk each feeding, thru the nipple shield. She gets real fussy and is very worked up and hungry before feeding but then after a couple of pulls on the breast she often seems to forget what to do and gets fussy and crying again. Any advice?