wheat allegy or Celiac?

My son was suffering with bad eczema and when he was weaned he had an ellergic reaction. We found out he was allergic to milk, egg and wheat and so he was put on a diet avoiding these.  The trouble is his wheat free diet is also gluten free but every now and then he has bad nights with high temp, stomach cramps and lots of wind. wheat was the last thing removed from his diet and on its removal his eczema improved and his stomache cramps also improved. I've been told its hard to get a positive test for celiac if you are on a gluten free diet can anyone offer advise.  My son has very sensitive skin as he reacts to these foods when he touches them, he doesn't have to eat them.