Ds1, now 14 has Aspergers and had very similar symptoms to your ds, with the addition of never having solid stools from when he was weaned until we removed gluten from his diet as a trial - until then we kept being told that it was 'toddler diarrhoea'. The difference was amazing, the diarrhoea stopped and he grew faster in that year than he ever had before (we was tiny for his age).
I would say though, don't do what we did, because we had to put him back onto gluten so that he could be tested for Coeliacs and he was so ill after he went back onto it we nearly called the whole thing off. Then he caught Norovirus the week before the blood test and hardly ate anything for most of the week, resulting in him not having enough gluten in his system anyway.
They did the test and it was negative, although they thought that was possibly because of the norovirus making the sample invalid, but we were advised by his paediatrician to keep him gluten free anyway, as the improvement both health wise and in growth etc had been so marked.
We were given the option of repeating the blood test, but to be honest, we really couldn't face making him ill again by putting him back on gluten containing foods for several weeks and we wouldn't put him through the biopsy test anyway, as he wouldn't have handled it well (he has health anxiety as it is).
Paediatrian and NHS dietician agreed a gluten free diet was the way forward and that is in both his medical notes and his school statement. He only has to get a bit of gluten contamination for his symptoms to flare up so it was obviously the right decision for him.
He does get stomach ache due to anxiety, but it's upper abdomen and caused by reflux. When his anxiety is really high he regurgitates small amounts of his meals and develops a bad sore throat.
I would speak to your GP about the possibility of a Coelia blood test, as if he's currently eating normal amounts of gluten containing foods, other than the fact it involves a needle, obviously, it should be an easy thing to rule out.
If it's negative, but you suspect intolerance, rather than Coeliacs, you could still try reducing the amount of gluten he eats by substituting some of his usual gluten containing meals with some free-from products eg bread, pasta, gf oats for porridge and see how he goes. Going gluten free is only a problem if you eat lots of shop bought manufactured rubbish, which to be honest is pretty dire anyway. If he eats plenty of fruit and vegetables changing to gf pasta and bread shouldn't be too much of an issue.