Why Am I Bleeding Again A Little After Two Weeks Of Taking Primolut-N While Taking Thyroxine For High TSH?

Hi, I am 29 years old unmarried. I got periods for 14 days and doctor prescribed me to take primolut n for 21 days. Today is my 18th day of course, i again got periods. I am taking thyroxine 75 mg also from 2 weeks TSH is 14. Kindly help me to regularize my periods