why my 3 month old baby is so thin. her weight is around 4 kg. She is on mother's milk. should I give her lactogen formula or kept feeding mothers milk

A. CF to see how much as your child gained in these three months it should be at least 1500 g in three months if it is like this then this weight is justified otherwise I would recommend you that yes you can start with formula feeding but go for a better one like similac or aptmil gold