My 3.5 week newborn breastfeeds. We are beginning to introduce one bottle of expressed milk to her nightly (so husband can get in on the feeding), though would like to have containers on hand for the holiday. How often can I pump (manual) w/out fear of not having milk for baby? Is there a duration of time it takes to produce more milk after expressing? My daughter will nurse roughly every two hours after completing her feed (though, is experiencing a growth spurt).