You have not mentioned the age of your son.
For vomiting zofran
Just gently press his tummy to see if it hurts some where.
If he cries or winces when you touch him, its better to have him seen by a Pediatrician
If vomiting persists or it is yellow (bile stained) you must see your Pediatrician to get any surgical causes ruled out.
Growing pains will not cause such a severe pain
that the child will wince.
Hope my answer helps you.
Wish your son a speedy recovery.