Home pregnancy tests are sensitivity to approximately 35IU HCG and serum blood tests to approximately 5IU. If your last unprotected intercourse was on 7/3, and you ovulated leading to conception on or about this day, your pregnancy test should have started testing positive on or about the 14 of July. Although statistically possible that you could test negative over a month later, this is almost impossible. Therefore, you are not pregnant. The probable reason why your period has not come in because you have started BC which may allow you to completely skip periods even though you are not pregnant.

Julio C. Novoa