MY SON HAS SEVERE STOMACH PAIN, CONSTANTLY THROWING UP, UNABLETO

MY SON HAS SEVERE STOMACH PAIN, CONSTANTLY THROWING UP, UNABLETO HOLD ANYTHING ON HIS STOMACH, ALL TEST HAS COME BACK NORMAL, THIS OCCURS APPROX 3-4 TIMES YEARLY, AND HAS BEEN HAPPENING FOR ABOUT 5 YRS NOW, NO DR'S SEEM TO KNOW HIS PROBLEM..PLEASE COULD YOU GIVE ME SOMETHING TO GO ON...THANKS