Thanks for your query.
If you have used the birth control pills as prescribed, regularly, without missing a single dose, they offer you almost 95 % chances of protection against a pregnancy
Also, having sex on the 4th and 5th day of the period itself has very less chances of resulting in a pregnancy.
However, to be absolutely sure, continue taking your birth control pills as prescribed, and be very sincere with them
In the rare event that you DO miss a period, please take a home urine pregnancy test at the earliest.