Confused and worried. TMI

Hey ladies! So i skipped my period week pills n started a new pack. I had the breakthrough bleeding already and i should be starting this packs period pills friday. About 2-3 weeks before i skipped them i had unprotected sex but he pulled out. And tonight i went to wipe and there’s a drop of red, nothing when i peed just when i wiped. So my question is how likely is it to get pregnant on the pill and why did i get this one random dab?