4th month regression help.

My boy currently 4mth 24day.Since 3 week ago start playing with milk and not drinking much. Will only drink when sleeping and sometime can't finish. When awake will drink abit only and play with milk. Has been going to IFC for 2 week. Teacher complain within 1 hr need to warm milk 3 to 4 time for him to finish. Today saw the up last 2 fed left about 40-50ml. Teacher ask me how and I also don't know. He is still active at home. Should I bring him to PD or any mummies out there got better solution. #pleasehelp