What Causes A Delayed Menstrual Period After Taking I-pill?

Sir..i had sex with my girlfriend a week back. She then ate i-pill within 5 hours. The next day we again had sex and she again ate i-pill within 5 hours....She was supposed to have her period on 20th...but today its 23rd and she had no menstrual periods yet. Her periods comes on time but its not the case this time. What is the cause according to you and what should we do???
Is she pregnant??