What Causes Irregularities In Menstruation?

Hello Dr. Its been one yr im married and I have not conceived yet... but my periods was skipped for one week, later for 12 days and for 18days in d beginning of our marriage. ... later on my menses s regular. .. nw it s been 12days I have not got my menses. .. n I don t feel any symptoms also. ... I have used pregnancy kit and negative... I have a dought whether I will have urine infection. .. pls suggest ...