Confused

My period is due n a wk. ovulation happened last Sunday I'm assuming. Didn't really pay attention so much this month but I had unprotected sex that Monday. Woke up early this morning with a brown/pink discharge. Hasn't been heavy jus very noticeable when I wipe. I've been very gassy with a little bloating but the craziest part is I usually have sore/tender breast right after ovulation which I kno is a sign my period will start soon. My period isn't due till December20/21. Wat am I experiencing? Earlier period or pregnancy?