type 1 diabetic son with joint pain...celiac??

my son is 3 and has had diabetes a little over a year now.  he has had sporadic, sometimes debilitating "bone" pain...usually right below the knee, the top of the foot or around his elbow for about 8 or 9 mnths.  he also has abdominal pain that can be pretty severe but all of these things seem to be temporary.   he did end up in the hospital for refusing to walk on his leg for 24 hours and ended up having an effusion in his hip joint but i dont think that is related to any of the other pain.  sometimes he wakes up in the middle of the night screaming in pain.  he has had 2 tests for celiac (standard blood test) and both were neg.  i have heard that celiac can present with these types of symptoms and am wondering if perhaps he has it and it is just not showing up in the standard test.  we have considered going gluten free but it seems like a big change for our family.  it seems alot more expensive and we are already strapped and have 5 other children so paying 3-5 dollars a loaf for gluten free bread doesnt seem worth it if i am not sure that he may have celiac.  any experience with this??  does it sound like the manifestation of celiac or maybe something else??