Why Is My TSH Level Still Increasing Despite Gradually Higher Doses Of Thyroxine For My Hyperthyroidism?

Hi Doctors, I have Hyperthyroidism. At first, I had around 6.5 level TSH and took 12.5 mcg thyroxine tablets as prescribed by the doctors for 5/6 months continuously and was controlled for some time but suddenly after 5/6 months, it increased to 12.3 level TSH and again I took 25 mcg tablets for 3 months but after the latest report my TSH level has risen to 13.6. Now I m taking 50 mcg tablets. Can you please tell me why my thyroid level increased? Haifall is the symptom. also have vitiligo due to which Thyroid appeared in my body as an auto-immune disease told by the doctor.