Breastfeeding and storage. Doesnt drink.

My baby drinks fine in the morning usually he is a slow sucker and he is fuzzy in the evenings and cries when drinks from me. If I thought to give formula milk he spits up. But drinks my mother lk ok. We have changed the flavour of formula milk too . Still.doesnt drink . If I pumped my milk.and gave on a bottle she drinks. As in the evenings all be she wants.more me ll and cries I do not know what to do. She doesn't drink doula too mad cries a lot m eventfmi pump I get only 20!ml milk . Can u also tell me hw long can I store milk I pump for feeding in afternoon in room.temp. sometimes she takes four hrs to wake and I canmot give the pumped milk. Plsntell about storing and using of breast milk as I have her naming function .on her 30 th day of birth and did not want her to be fuzY ..