What Causes Irregular Menstruation?

I am a lady of 30 yrs i am not menstruating for long period of time i dont know what is happening n my life since 2007 i can count how many month that i saw my period but this year i menstruated on January 08 only 4 days since then i never saw my period,i am not using contraceptive,i am still a virgin i dont have a boyfriend.please help me and i am not sick.