Pregnant?

Okay so 8 days ago I had unprotected sex and he finished inside me. My period isn't supposed to start until next Monday (so 13 days after I had sex) but today I started bleeding but it wasn't heavy enough for a tampon. It had moments where it was kind of heavy but still light. I been using panty liners it's so light. Anyway I don't know if it's implantation or my period.