My periods stopped long before I was diagnosed with Graves and Hyperthyroidism and I had RAI 6 months ago.
I went for hormone tests this week as I heard that thyroid disorders can cause fertility to drop and periods to cease or become irregular.
My results showed I am well gone past the menopause!
I am 48 years old and havent had a period since I was 43.I wont get any now either.
I have seen others post that they cannot fall pregnant because of the TSH being out of range (either hypo or hyper).
I would say the best thing to do would be a pregnancy test and if negative, see your Doctor as the RAI can do a lot of things to your body.
Chances are , your periods will resume to normal once your TSH does.
In regards to BC, I would ask your Doctor whether to take or not.
My gut tells me (but don't have any knowledge to back it up) that your body might have been shocked by the RAI and messed up your period. I always took my BC whether I had started a period or not (but I was taking it to regulate my periods anyways). Is it possible you are pregnant? If it is a possibility I wouldn't start until you had a negative test.