baby only drink milk while sleeping.

My baby (Formula milk) doesn't want to drink milk when she is awake. We can only fed her by slowly removing her pacifier replace with milk bottle when she sleeping (not Everytime success). Have been 4 mths she behaves like this. She is turning 6 mths soon, only drink 500ml++ every day. Last time she can drink 130ml but now dun know why she easily choke by the milk end up can't finish the milk..cause her milk intake drop from 700ml to 500ml++ . Any mummy experience same?