pregnancy

Is it possible to be preggy even if your using a contraciptive?i used a pills.but i stop taking it recently, last of of november.because i feel something.Sept my monhtly period wasnt come until november 2nd week that why i decided to hve a pregnancytest, but result is negative.is it possible?i hd to ask this bcause i dont knw how month old is my tummy.it going bigger already..thank you!!