Thanks for posting your query.
With the available described symptoms, there could be possibility of constipation
due to weak development of gastrointestinal neuronal system.
You should consult with pediatric surgeon/ gastroenterologist and should go for thorough check up.
You should also go for x ray
abdomen to rule possibility of Hirschsprung's disease.
You should give him soft diet
along with plenty of water.
As per thyroid
details are available, it appears to be normal.
You should continue feeding habits.
Dr. Mayank Bhargava