Stomach ache from last two months.

Son is type 1 diabetes from August 2020. HB1ac is 6.4 done in March 21. He had stomach infection ( vomitting, loose motion, stomach ache ) in February 21. After taking treatment from Pediatric dr, vomit, fever and loose motion were cured but he is still complaining stomach ache till now. We had done Iga test for celiac it came negative. He mainly complains stomach ache at the time of getting up in the morning and around sleep time. And sometimes he also complains stomach ache before going to poty. No diarrhea, no vomit only stomach ache. Stomach ache is around navel area only. He is also looking weak and no weight gain from last two and half months. His diet is normal. Please guide anyone who is Pediatric gastrologist. Thanks