Pregnant because i started the second pack at a wrong time?

i have been on yasmin for 2 months now.  i had my period after my first pack but it was 3 days delayed and it lasted only for 2 days.  is this just normal? coz i had my period before for about 3-5 days.   one more thing is i should start the second pack  on a saturday but accidentally i started it on a sunday and went thru all the 21 tablets but i took them at the same time each day.  i had an unprotected sex after 4 days on the second pack.  it is now the 2nd day of my pill-free 7 days.  i am experiencing some bloating and lower back pains.  could i be pregnant because i started the second pack at a wrong time? or its just effect of my period that's should be coming either tomorrow or the next day? please i need answers...thnx