breast milk ➡️ formula

My LO is EBF and I have just returned back to work. Baby girl will eat 5oz every 3 hours   but I can't seem to pump enough to keep up with her. I had to supplement with formula (enfimil gentle ease I believe) but every time I offer her formula she will gag and spit it at me. I have tried countless times to offer it to her and she refuses. My question is, how do I produce more for pumping, and is there any other kind of formula that might taste more like breast milk?