Birth Control Question..

How long does it take birth control to protect you from sex? My boyfriend and I had sex.. And I've been taking my birth control for almost a month now.. But 3 weeks before we had sex.. We had unprotected sex, but made sure that he pulled out way before.. And I jacked him off so he could already pre-cum because pre-cum still carries a small amount of semin.. I took a pregnancy test and it came negative but I didn't wait to take it.. I took it like a day after.. We tried to use a condom but it was way too big for him, and I didn't want it to slide off his dick.. Do you think I'm pregnant?