Hello! I have a 6 month old girl for whom i pump everyday at work. but lately some of my milk is just not freezing! Its not all of it... just some of the bags do not freeze. I store all of them in presterilazed bag that you can but at babysrus and keep them in a little "box" separated from the rest of the stuff in the freezer. I dont know if i could still use that milk or its not good.... Does anyone had that problem before???? What should i do???