mayb your boy not used to the milk. that time my boy got diarrhoea (watery poo) many times a day, my pediatrician ask me to reduce the milk. e.g. 240ml shld b 8 scoops (for mamil gold). give 5-6 scoops instead. will take some time before they recover though.
till now, my boy recover already, the max scoop i gave is 7 scoops for 240ml.
you might want to try that. reason being, milk is oily. so baby's stomach might not b able to take it. heaty also. also, let him drink more water to prevent dehydration esp if his motion is diarrhoea type, watery type.
cant give much advice 'cause my boy only 7 mths now.