Why There Is Delay In My Period?

Hi . My age is 27 yrs. normal female. I took contraceptive pills for the first time from 11 oct 2011 onwards in order to prevent pregnancy. I had my period started on 1 oct 2011 & I had unprotected sex with my husband from 5th oct to 9th oct. My next period was due on 28th oct but its almost 29th oct over & my periods have not yet started . Also I did not complete the contraceptive pill course .I stopped taking it after the 21 st tablet. Still 7 tablets are remaining in the pack. What are the possibility of this delay in my period ? Is it because of the medicines ? If yes, then how long it will take to start my periods or is there a chance of pregnancy.. Your advice on this matter will help me...Thank you