What Causes Delay In Menstruation Other Than Pregnancy?

sir i'm a newly married couple and my question is my wifes period cycle is of 25dayz, and last time she got her period at 12dec,11. But till date she doesn't got her period but she has a symton before periods re pain in chest. my wife hav pain in her chest , and we hav a protective sex 1dayt before her period and she was travelling this month more than she does .I want to knw why the periods are not happned? reply