An emergency contraceptive pill, such as i Pill (levonorgestrel), can temporarily alter your menstrual cycle, causing your period to come earlier or later than usual. However, pregnancy should still be ruled out because levonorgestrel does not prevent every pregnancy. Since your home pregnancy test was negative on the 11th day, repeat the test now if it has been at least 21 days since the unprotected sex. Pregnancy tests are most reliable from the first day of a missed period or at least 21 days after the last unprotected sex. A negative test taken too early may not reliably rule out pregnancy. If the repeat test is negative but your period still does not start, consult a doctor or gynaecologist. They may recommend another pregnancy test or further evaluation for other causes of a delayed period. Seek urgent medical care if you develop severe lower abdominal pain, fainting, dizziness, or unusual vaginal bleeding, particularly with a missed period.