Brown spotting on pill HELP!!!

Hey ladies so I’ve been on the combination pill for years and I’m good at taking it. This past weekend i was in a wedding party so i took my pill a little later then normal for a few days. I have some brown spotting, but i am sexually active and about 2-3 weeks ago i had sex on my placebo week and my boyfriend came inside. I am worried about pregnancy. I have about 2 weeks weeks left of active pills before my period. Is there a chance im pregnant? Or am i having breakthrough bleeding BC of some time fluctuation in pills?

Ps : i took a pregnancy test it was negative although I’m not sure if it’s even accurate with the time frame I’ve described.