What Causes Absence Of Withdrawal Bleeding After Stopping Birth Control Pills?

Hi, I went on noriday about 5 years ago. initially I was bleeding lightly all the time and so the doctor put me on double dose so I was taking two per day, during this time I did not experience any periods... however, if I was ever late taking my pill or missed one accidently I would get a withdrawal bleed for about 4 or 5 days at a time. Now I have come off the pill all together as me and my partner are trying to concieve. since stopping the pill this time I have not had a witdrawal bleed and no sign of any period, pregnancy tests have been negative although it has only been two weeks since I took the pill. could I still be pregnant and would it be usual not to experience any withdrawal bleed within this time?