What Causes Missing Periods While On Hyperthyroidism Medication?

hi i m 33 years old female with hypothyroid problem since i was 10 yrs. I m few weeks late for my periods. It is fairly normal and my cycle is of 26-28 days.
I got my tyroid test done t3 and t4 are normal but value of TSH is 29. I am taking eltroxcin 100mg 1 and a half tablet.
Is the cause of my missed period is thyroid or can i be pregnant.