When my daughter, Elyie was 5 years old, she started complaining of stomachaches a lot. Her pediatrician put her on reflux medications.
After some time of still complaining, I took her to a GI specialist, who still thought it was reflux. Her pain was at her belly button, which to me did not sound like reflux, but he wanted to add two medications to what she was already taking. We did this for another year or so until the stomachaches were daily and diarrhea occurred multiple times a day.
I was getting very concerned by this point and took her back to the GI doctor. I told him that I was taking her off all her medications and I needed him to find out why she was having such bad diarrhea and stomachaches daily. He did a stool sample to check for blood and a blood test.
Three days later, he called me very apologetic for not having done this blood test sooner, and that she was positive for celiac disease. We confirmed 2 months later with an endoscopy. We have been gluten-free since then. She is now a thriving 10 year old!