Breastfeeding..

The first few days after my daughter was born I was breastfeeding. I am not making enough so I am having to supplement with formula. Meanwhile I am pumping so I can tell how much I am making compared to how much formula she is getting. Lately anytime I give her breast milk she seems to spit it up and not keep any down even tho when she latches she keeps it all down and has no issues. She won't take it if I warm it with hot water. She wants it still pretty cold. Any clue as to why she wants it cold or why she would spit up more with pumped?