Almost 4 months head issues

Sea

Okay so all my other kids could sit at this point. My baby can barely hold his head up he can but not for too long. The doctor didn’t seemed concerned but I have friends with kids much younger and they’re sitting up unassisted even. He’s a very sleepy boy sleeps like 17 hours a day. I do tummy time all day every day but he just falls asleep. His birthday is April 25 someone cure my worry and tell me their baby is the same and it’s normal 😭