my wife had a normal delivery of a boy. our baby is now 38days old. at birth he was 3kg and now he is 3.400kg. during the initial days my wife was breastfeeding him after every 2 to 3 hours for 20mins and he was fine. but recently we have noticed that even after feeding him for 20mins he still cries and as soon as we put him on breast he starts to suck on milk. we doubted that the breast milk is not enough and to confirm that my wife expressed breast milk for 20mins manually to check the quantity and found it's only 18ml . kindly advise.