My son has had trouble with his tummy since he was born. After seeing a GI we removed dairy from his diet and his bowel movements improved. He vomitted with egg so that is excluded too. He moved on to soy milk at 16 months old, but at 2.5 years old he started saying his back hurt and his bowel movements became very loose, with mucus, smelly, and frequent. He sleeps lots in the day. Eventually they said exclude soy then wheat. He improved dramatically. After 4 mths with no soy or wheat (and dairy and egg) he started complaining of tummy cramps, now stools are mostly loose,2 or 3 per day. Still having tummy pain. He gets very tired doing nothing. Tried wheat again to test for Celiac but doesn't seem to have a problem with wheat. Had upper and lower endoscopy and SBFT all negative. It seems to be a cycle. Could it be Crohns?
I'm sorry to hear about your son's tummy troubles. While this isn't easy for him. I know it's hard on you to see him in distress. Unfortunately, there is simply no way we can tell you what it wrong with him. If you feel that the GI you've been taking him to is out of options or no longer being helpful then I would suggest it's time to take him to see another pediatric GI.
You said he was tested for Celiac, but have you removed ALL wheat from his diet for at least 2 months? Most of the blood tests that are done test only for food allergies, they cannot test for food sensitivities which can cause serious symptoms in some people. The only fool proof way to really test for food sensitivity is to do something called an Elimination Diet - you can look at some of my older Shareposts on this site which explain this diet, or you can go to the web site www.breakingtheviciouscycle.org to read a little more about it.
BUT, before making any drastic changes to his diet, since he is so young, you must talk to his doctor first and do this under a physician's supervision.
Good luck to you.
I had exactly the same problems with my son for many years. I eventually discovered a lab (Enterolab) online and had them do a gene test for celiac (he'd already had a biopsy and blood testing for celiac which were negative). The celiac gene test came back positive. The other celiac tests are not always accurate so you really should look at him getting the gene test (they send you a swab which you rub inside the mouth and send back to them, cannot be any simpler). After the positive result I immediately took him off of gluten completely. It's not the easiest thing in the world to do but it's worth it in the long run as your child will feel great. Give it a while (it took my son at least 8 months to start feeling better). Try it, it may just be the underlying problem. Good luck.