Newborn abnormal test

So my baby tested abnormal for thyroid levels. She has been producing more so her pediatrician suggested she may have hypothyroidism. She has done the test twice, and both abnormal. He mentioned he talked to an endocrinologist and told me that she would redo the test again and than based off that she would go see the endocrinologist. To whoever has hypothyroidism, how soon did u start on treatment, i feel like my baby should have already she is 4 weeks but online it said start treatment as soon as possible.