My Period Ended April 17, I Had Unprotected Sex April

my period ended april 17, i had unprotected sex april 18. later that same day i took a birth control pill at 11:43pm then took a next one 11:37am on april 19 (these were not morning after pills). however,april 23, i started experiencing bleeding but like in a brownish color and this morning i woke it was more than the previous night. Help! what could this be?