Me and my partner had sex 4days ago, i've been bleeding for 3days since but i've just had a period. what is happening?

Cervical trauma?: You basically started bleeding after relation and so it not possible of being pregnant just yet from this episode. The bleeding is likely resulting from cervical trauma--i.E the tip of the penis hitting the cervice repeatedly during relation. This usually resolves spontaneously. If you have period regularly before this, i suggest doing a hpt (if u had sex before this too). Consult doc. Good luck.