my baby is 3 months 22 days old. Her neck muscles are weak. She could not hold her head up and she is 4.3 kgs

A. Mostly Kids have a stable head by the age of 3 to 4 months maximum so wait for you don’t like a week to 10 days more still if the head is not stable then you should consult your paediatrician to get it checked because that way you will have a clarity about it because if there is issue you will come to know it in the right time