I had thyroidectomy for half gland last year and had regular period ever since, but now it is late?

I am 22 years old and I had rhyroidectony for half gland last year 2016 July I had regular periods. But this year 2017 October I didn't get my periods yet ?? What was the reason am so much worried am 22 years old and not married am not able to concentrate on my studies also what shall I do now to get periods back