Can Pregnancy Be The Reason For The Delay In The Periods?

doctor, me and my girlfreind had an unprotected sex on 31of december 2009. she took an ipill for safety after that she had 4 periods. we again had sex on 10 april 2010 with 2 condoms and she also took an ipill for an xtra safety. on the very next day (11 may) she had her periods and the duration of the period was 6-7 days. now in may her due date was 11 may but she did not have her period yet. is she pregnant? does period usually last for such days? what should i do now. can she b pregnant of that december sex?