What Causes Menstrual Delay?

I am 27 years married for 4.5 years. I and my husband are trying for a baby after 1 year after our marriage. I am suffering with irregular periods. I underwent histo laproscopy and DD&C in July 2011. The diagnosis report shown no problem. I had to travel out of station with my husband for 3-months; so doctor advised me to continue Profert-f for 3-months. My last period was on 31-oct-2011 now it is almost 42 days I haven't got my period yet. Please advise me on what should I do. I am worried.