Hello Dr, my baby is 15 days old and weighs 3.1 kg. i breastfeed him mostly and he keeps crying and does not sleep most of the time. It seems his stomach does not get full so I give him formula milk quantity around 40 ml. Sometimes he sleeps after that n sometime he still opens his mouth after that. So m really confused how much formula milk is required for 15 days baby weighing 3.1 kg n is it ok to give formula milk after baby is breastfeed or it can make his stomach upset. Thanks in advance.