My daughter is the same age. Last August she saw a gastroenterologist who diagnosed her (only through questioning,not testing) with acid reflux. She put her on Zantac, which seemed to help a little, then stopped working. The doctor ordered an x-ray which showed that my daughter was extremely constipated. I mean she was totally full of poop!! She never showed any signs of constipation,,,no hard time going, and she seemed to go often enough. She complained of belly aches constantly, and I started to think it was nerves, also. Now she's on Miralax daily, and she's perfectly fine.