My son has had hypothyroidism since birth medicated bowel problems from 12 months consultant says unrelated to thyroidis, due to being treated is this?

Mild hypotonia, low: Muscle tone from hypothyroidism affects smooth muscle of the intestines & causes chronic constipation. Seek referral to a pediatric gastroenterologist to see if he needs a "clean-out" before using MiraLAX (polyethylene glycol) to keep stools soft for at least 6 mos. Even treated, kids with congen. Hypothy. Can have learning disabilities. A pediatric endocrinologist manages meds & follows labs here in the us.

If lab tests for: Thyroid normal on his thyoid treatment, then look for other causes of his symptoms.