Baby kurang menyusu

Hai..my baby is 4months old..by feeding chart kat susu dia supposed dia mnyusu 5oz/6 times a day..since dia turn 4months hari tu I dah up kan from 4oz to 5oz..dia susah nak habiskan..so I turunkan smula ke 4oz..pun skrg susah sgt dia nak habiskan..stress tgok susu x abes..pernah tak baby korang mcm ni..n what u do?