my girl, currently just over 4 wkks old, has the same issue and it was since birth. dr's advice was to burp baby well, especially if bottle fed. she is currently 4.5kg and at times, can drink up to 120ml at each feed and was on 90ml since being discharged from hospital. other than burping, i try not to lay her down too soon after each feed (started with holding her for 10 mins and now shortened to 5 mins before laying her down). i find that it helps when she lays in a tilted bassinet instead.