Pregnant or not?

On June 20 (the start of my last fertile window), I had sex with my boyfriend. I don't take birth control, but he had a condom on. As he was ejaculating, he pulled out and some semen started coming out from the bottom and got on me. Scared, I took Plan B two hours later. My period never came. I took some pregnancy tests a few days ago, and they all came out negative. Today makes it five weeks since June 20, and I took another test (still negative). However, I've also started experiencing some light brown spotting. I still haven't had my period, so I'm scared! Am I pregnant?