hello doctor, my son is 4 months old and his weight is 6.5 kg, last month his weight was 6 kg...he only gained 500 gm during the entire month. should I be worried, birth weight was 3.6 kg and baby is completely on breast feed, should I start formula for him. he wets around 20 nappies in a day and almost 4-7 bowl moments , he passes stool once in 7-8 days...he is very active and doesn't cry much ...pls suggest