Falling off the growth chart. Celiac? Endocrinology? Next steps?

[MomInTheMitten]

DS is 5.5 years old and is trending toward a drop off of the growth curve. His ped is recommending a recheck in six months, but of course, I'd like to get my thoughts in order and possibly take action before then. My instincts have been telling me, almost since his birth, that I haven't been giving him all of the help he needs to thrive. My questions are, do his symptoms sound like Celiac, something endocrine or something I have not thought of and where should I go from here? TIA!

His current/past symptoms include:
-short stature (about 10th percentile, declining percentile since birth, but hovered near 25% until last year).
-celiac body type? bigger tummy, littler bum and legs
-occasional irritability, resists new social situations and change. I looked into
SPD for a while but this didn't seem to fit for the most part.
-recovering picky eater. Had a varied diet and a decent appetite until about 2 years (weaned just before that), but appetite declined and number of accepted foods drastically dropped (mainly dairy and carbs, 1-3 items in protein, veg and fruit categories). Very focused on cows milk from 2-3.5 or so. Accepts a better variety now. I'm happy with his present food intake (accepts 6+ items from each food group, and a variety of textures). Still dealing with difficulty focusing and self-pacing at mealtimes (dinner in particular).
-had constipation/encopresis issues from 3.5 to 4.5 (stemming from time baby brother was born, treated succesfully (?) with stool softener, fiber in diet and regularly scheduled potty times).
-had green mucousy stools with occasional blood from 2 mos to introduction of solids at 6 months. Allergy tests and elimination diets did not yield any answers, ped suggested that he'd outgrow the problem. I've always felt unsettled about this.
-was a high needs baby

Other family notes:
-I also might have a celiac body type. Even at my most fit I have little pooch and a flat bottom with short legs
-I have a well-managed hypothyroid condition, began treatment for it about four years before DS was born
-I'm 5'5", DH is 5'7", so while we never predicted our children would be tall the change in trend toward unusually short is puzzling
-my mom is my height but my dad, brother and sisters are all taller than 6'; DH's family members are all shorter than average
-DH is extremely sensitive about his own height and wishes he would have been given growth hormone as a child
-DH seems to have some kind of gut issue. He's had issues with diarrhea since a gallbladder removal 7 years ago. GP is not worried but I wonder if he has a food allergy or gluten intolerance.
-our heritage is mixed European

[justmama]

My oldest child is 12 now and below the growth charts and has been consistently since about kindergarten.  She had gas/constipation/stomach pain issues as an infant that mysteriously resolved and appeared again in kindergarten and again mysteriously resolved.  I'm not talking an extended tummy virus time.  I'm talking literally nearly a year of pain, gas, constipation and other assorted issues that never seemed to fit any pattern.  She was a small 6lbs 5oz 40w1d baby born when I was 19.  She continued to be small but developed normally.  She began falling off the growth charts around 4 and never came back up despite years of trying on and off for months at a time to fatten her up both in healthy ways(avocado, smoothies, peanut butter, coconut oil, butter) and non-healthy ways(carnation instant breakfast, pediasure).  Nothing worked.  She's 12 now, extremely healthy(she jokingly tells us that her immune system has ninjas), and active and intelligent.  The only time we notice any issues with her health is when she gets the once a year cold or tummy bug that lays her out flat with hypoglycemic issues because of her very low body weight.  She was also extremely picky as a babe but over the years has developed quite a wide palate.  She much prefers fruits and vegetables over anything else still but she will eat just about anything you put in front of her now.  She seems to have outgrown any issues as a young child/baby.  She's still very thin though.  She's 12 1/2 years old, 5foot 3inches and only 70lbs.  Her pedi is comfortable with her weight as long as she doesn't lose.  If she maintains, she's okay.  But she gains EXTREMELY slowly.  She's gained 4oz in 6months.  According to her pediatrician, most of her same-height peers are an average of 20lbs heavier than her.  But she's so healthy.  I think she just outgrew any sensitivities she had as a child.  I'm not saying she didn't have any or that I feel like I handled it well but I was a first-time mom and only 19 years old.  It seems she has developed well and become quite healthy and strong.  Maybe there WASN'T anything wrong with her as a younger child.  I don't know.  Maybe she's just a very small and thin person.  Maybe she'll put on weight when she hits some of the later stages of puberty.  I don't know.  But she's okay now.  Maybe your son will be similar.