Suffers Congenital Hypothyroidism, On Thyronorm. Irregular Bowels, Tried Glycerine Suppository. How To Cure Constipation ?

my 45 days old infact suffers from congenital hypothyroidism and is under treatment with thyronorm 37.5 microgram per day. he is suffering from irregular bowel movements, gas and stomach pain. he strains to pass stool, makes sounds but no stool comes out, he starts crying. i had to give glycerine suppository to make him pass stool. he cries after most feedings, especially in the evening, only decolic drop gives some relief. how to cure the constipation? please help.