my baby boy is 1month 8 days old his birth weight was 3 kg and now he is 3.5.kg is it normal, he is on BM

A. Yes it is completely fine a child should gain about 500 g in a month so looking at that your child is about 100 kg behind because every week it should be of minimum hundred grams can go up to 150 g also but as of now this is average good