What Causes Delay In Menstruation Other Than Pregnancy?

Hi doctor,
I got married one and a half years back... Till then i have had regular periods... But for the past 7 months i am having irregular periods.. The last time i had normal periods was on April 2010.. Then i didnot have them so i consulted my doctor on June and was prescribed anofer, cycloreg tablets... After these medications i had my periods on June... But again i didnot get my periods in July and August... So again in took the same medications... I got periods in September... Now i didnot get my periods in October... What do i do? What must be the reason?? Please help us?? We are trying for a baby since we got married...