Well, my daughter has Celiac disease. She's 16 months old. She was diagnosed around 9 months old. Before diagnosis, she had CONSTANT diarrhea (several times a day or more) that was very bulky, pale colored, and greasy. She was almost always in pain, and would just lay on the floor and throw fits...inconsolable. She had...oh, there's a name for it...something like dermatitis herpatoformis (that's probably wrong) but basically, she had an eczema like rash behind her ears and in the crooks of her elbows that would just become open sores and bleed. It was awful. She was always fussy, always grumpy, never smiled, and quit developing, essentially...wasn't putting on ANY weight or growing any, wasn't walking, talking, teething, etc.
After removing gluten from her diet, it was literally a miracle change in my baby. All of a sudden, I had a happy child I'd never known. Her skin cleared up, except for one spot on her arm that I think is just too damaged. We're still working on it. She isn't in pain. She doesn't throw fits. She immediately started walking, talking, teething, growing, gaining weight, eating well, drinking well, laughing, playing, etc...
...and for months, I just thought I had, honestly, a difficult baby that I was SO concerned about because I just knew something was wrong.
Why bother with the doctors? You can do a gluten free test on your own...simple remove all the gluten. I'll warn you, though, that it will be difficult at his age and that gluten is hidden in ALL kinds of foods. If you'd like a list that I've made myself of all the foods my child can and can't have, message me. I've done extensive research for her sake, because she is so sensitive, and we do not mess up her diet. I am also on her diet because I am still nursing.