YES, PLEASE HELP. MY SON IS 15 YEARS OLD AND

YES, PLEASE HELP. MY SON IS 15 YEARS OLD AND HAS BEEN COMPLAINING OF PAIN IN HIS LEGS AND FEET. SOMETIMES ALSO HIS BACK. HE SAYS HIS FEET HURT TO WALK AND HIS LEGS ARE ACHIE. HE WALKS WITH HIS FEET TURNED OUTWARD. WHEN HE WAS LITTLE THE DOCTOR TOLD ME HE WAS FLAT FOOTED. WHAT IS CAUSING THE LEG PAIN AND SHOULD I TAKE HIM TO A ORTH DOCTOR?