my baby boy's birth weight was 3kg, every month he was gaining 1 kg till 4 month but after that his weight gain is slow and now he is 7.5 month and he is weighing only 8 kg , is this something to worry about

A. So your child was practically 7 kg by the age of four months itself and after that your child gain anything so it’s very unhealthy because the child should at least gain 500 in a month I would advise you please talk to your doctor about it