Seem to lose interest in milk...

My LO is turning 4mths in less than 2 weeks. We realise that she seems to get distracted alot when feeding (she mainly on BM except for night feeds) recently. She will arch back, push away or play with the bottle teats. Eventually we will have to split 1 feed into 2 or 3 times before we can complete. I looked up online for reasons why but seems like nothing is really matching... what comforts us is at least she is sleeping, wetting her diapers and smiling well. But we are still wondering why is she not drinking properly...