Flat Head. Is this hereditary

My son just turned 16 months and my wife and I notice that his head is still flat. It has some curve to it but is noticeably flat. He never lays on his back and from an early age say 5 months we adjusted his head while sleeping and did more tummy time. IS this hereditary because his granfather has the same thing. Not sure what to do. Maybe his head is still growing and will fix itself.