If the birth control pills have been started on the first three days of your period then you are immediately protected against pregnancy and need not worry about any additional contraception.
In case, the birth control pills were started later than day 3 (day 1 is the first day of your period) you are protected against pregnancy after 7 days of pill usage. In that case I would suggest that you take an emergency contraceptive pill within 72 hours of the unprotected intercourse. Getting an intrauterine device inserted is also an effective emergency contraceptive method that is effective for upto 5 days after intercourse. Taking an emergency contraceptive pill may alter the hormones of your body and may advance or delay your periods. You might even experience some intermediate spotting or bleeding. Do not worry in that case as it is mostly a side effect of the pill and is self limiting. In the rare event that you altogether miss your periods, take a home pregnancy test to find out whether you are pregnant before you start a new pack of birth control.
Hope you find this information useful. If you still have any doubts about the correct usage of birth control pills, I suggest that you visit a family planning center for expert advice.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.