my baby is 4 month s old weight 5 kgs only not gaining weight and every time vomit milk what to do to stop vomit of milk

A. dear Mum baby should gain atleast 500 gram per month and should double the birth weight by 6 months or less vomit is common burp keeping the head and chest at a level higher than stomach helps to reduce vomit. if baby is passing urine more than 7 times a day is active and alert and gaining adequate weight ,at least 500 gram per month then do not worry