Is there a cause for concern if my 4 mth old is unable to hold up his head steadily?

Hi, my baby boy is 3 mths 25 days, but he is still unable to hold up his head steadily and will always need to be supported. Have tried daily tummy time and at times, he will hold up his head for a short while, though most times he will just be wailing and lying there. Have also tried putting him on his back whilst he hold on to a bar (with our help) to lift him up (similar to doing sit up), but his head will just tilt backward. Have brought him to see the paediatrician 2 weeks back and doc’s advice is to monitor till he is 4 mths. Baby is reaching 4 mths and it’s getting worrisome. #1stimemom #advicepls