pumping and supplementing

I need help 😩 I feel helpless.. I pump and feed my LO from a bottle, she could never latch properly so I gave that up. However we supplement with formula if I can't pump or don't have any supplied. My LO started out on similac pro advance and seemed to be spitting up a lot but we thought it was because the pediatrician was having us feed her more because she wasn't gaining weight. A week later we changed her formula to enfamil gentle ease and again she spits that up. She is not a good burper. She farts a lot but you could burp her for 20 mins and nothing. Could it be that or the formula?? Help!! I feel like she's starving when she spits the formula up.