E.B.
EDITED TO ADD: By the way, when my child was going through this (the constipation, the pain, the bowel issues), we found out she was severely intolerant to sorbitol. Sorbitol is a sugar-alcohol compound that naturally occurs in certain foods. In many people, it either doesn't do anything or relieves constipation. However, in some people, it can cause severe stomach/intestinal cramps, constipation and a great deal of pain. It's quite simple to eliminate and may be worth trying for 2 weeks or so. Sorbitol occurs in apples, cherries, pears, and plums (and therefore prunes, which are dried plums). It is also in red/purple grapes but not green grapes. So we only gave our dd pure white grape juice, and read every label (did you know that the first ingredient in things like Kiwi Strawberry Juice is apples?). We eliminated all sources of apples and all those sorbitol containing fruits. Instead of apple sauce, we gave her pureed peaches. Oh, and make sure your kids don't have anything artificially sweetened or "diet". Sorbitol is in many of the diet, sugar-free gums, sodas and foods. After just a few days off sorbitol, we saw an amazing change in our dd. She still cannot tolerate it. If she gets it by mistake, there will be cramps, pain, constipation, and many problems. You might try it! It certainly can't hurt, as you're only taking away a few fruits, it's a pretty easy switch.
I am glad that your son will be getting some testing done.
But please keep in mind that with many conditions or diseases or disorders, the symptoms are varied, vague, intermixed with other things, and they are difficult to unravel. Very rarely do you take a child into a doctor (I'm not talking about ear infections, I'm talking about chronic stomach aches or constipation or internal pains or strange symptoms) and come out with a quick diagnosis. It sounds like you were taken seriously (x rays were done, exams, etc). But now it's time to proceed to the next diagnostic level.
Do not get mad. You haven't ignored your child, you haven't been neglectful. You have done your very best to speak to doctors, to advocate for your son, to feed him well, and to care for him. So be proud of yourself for not stopping to search for answers, for continuing to take care of him, for being proactive in his care and being the kind of mom who doesn't give up.
My dd has 3 rare diagnoses and it took over 6 years to figure them out. Time after time she underwent tests, only to have them come out negative. Time after time I brought her to doctors only to be told "nothing appears wrong. I don't know what the source of her symptoms are. Try eliminating milk, or try this or try this." It often takes determination and perseverance and time, until you finally are sitting in front of a new doctor who says "hmmm, I wonder ..." and the light bulbs go on, the bells ring and everybody says "a ha!". And yes, sometimes it seems as though you have told the same story and related the same symptoms 300 times before, but this one time, you see a doctor who remembers a case, or who heard of this once, or met somebody ... It's the reward of not giving up the search. It's not anyone's fault, it's just that some cases are like untangling a huge ball of knotted yarn.
[By the way, a Celiac blood panel is not enough in many cases, to get a diagnosis. A biopsy is needed (it doesn't hurt). And ask for allergy testing too.]
Don't let this scare you. Of course, it's the natural response, but if it's Celiac or Crohn's disease, you'll learn new ways of cooking and eating, and there's support out there, and your son will be well. You sound like a really good mom, very concerned and willing to be your son's advocate. You are certainly not alone. Turn your fear and anger into positive determination to stay calm, to learn to manage whatever diagnosis is eventually given, to be your son's best medical advocate.