Hello and very pleased to answer you.
There are three types of hypothyroidism: primary, secondary and tertiary. In secondary hypothyroidism, the
pituitary gland does not control sufficient production of hormones by the thyroid. In other words, the problem does not come from the thyroid. The same applies to tertiary hypothyroidism (the
hypothalamus does not produce enough TRH,
thyroid stimulating hormone). TRH plays an important role in stimulation of the pituitary gland for the production of thyroid stimulating hormone (TSH).
In your case, with a low dose of
levothyroxine (50), your TSH level do not change, and clinically, you are always suffering from hypothyroidism, and normally as your levothyroxine is low TSH should be very high, but your nervous system does not interact with the problem, and the TSH do not change.
Than you have a secondary hypothyroidism or a tertiary hypothyroidism, and you need to consult an
endocrinologist to make all the things in theirs way.
Time to see the endocrinologist, I propose you to take 100 mcg day of levothyroxine.
May this answer help you and best wishes.