My baby (born at 39 weeks without complications, birth weight 3kg) is not rolling over. He is now 5 months 3 weeks and 8kg+ (height 67cm). He is on track for all milestones- babbles, smiles, responds to his name, sits for few seconds without support, holds his toes and tries to move to one side holding them, grabs things, etc. Except rolling over. When we roll him on his tummy, he rolls over on his back but he himself doesn't try to roll. Nor does he rolls over on his tummy from back. Is this normal?