4 month old refusing to breastfeed during the day

Li

After being out during the day for a couple days in a row my daughter had bottles of expressed milk. She is now refusing to breastfeed during the day. She fusses and cries as soon as I try to. Then chugs down a bottle. She also had her 4 month shots this week. Anyone else experience this? I am trying to pump and feed by bottle but can't pump enough. Doctor said to introduce formula :/