Hi, My Son Has Chronic Abdominal Problems-no Diagnosis-since He Was

Hi, my son has chronic abdominal problems-no diagnosis-since he was an infant. When he gets a cold it progresses to him bringing up mucus and then vomiting for a few days (was with diarrhea when he was smaller-he is now 9). more recently intermitent abdominal pain and foul smelling gas. xrays, ugi, u/s were negative and i am wondering if it may be celiac. i already avoid certain things that has caused him diarrhea or vomiting as a child (milk, red meat) but i am thinking to also include gluten. I would love any input i can get. Thanks