chubby baby

Hi mga mommies, my baby is 3 months old and the doctor said her weight must be 4.5kls but my baby weights 6.9 kls. She is on formula milk NAN Optipro one, nawala kc agad breastmilk ko? Im bothered na super fat na c baby at sumasakit na likod ko pagmatagal ko syang karga . Ito nga pala picture nya. May exercise ba for babies? Para maburn ang fats ni baby????