A.L.
is it his stomach or more over to the upper right? because that is where his gallbladder is and as you might know, bile is green..and it makes me wonder if the problem is more gallbladder/liver related than it is stomach problems. although, when your gallbladder hurts, it can cause a stomach ache as well.. have you noticed where on his tummy it hurts? when my son's stomach hurts, I have him point to which part .. if the upper part and he just ache, I know that that might be attributed to something he recently ate, vs the lower half which is usually something older.. by figuring out, what part of the tummy, this helps me to discover if he shouldn't or should have certain foods..
best of luck