Finish period and 4 days after that had sex should i do pregnancy test ? i take postinor?

Not clear on your exact question. Four days after your finish your period is often a time you could get pregnant. If you have Postinor, then it should be taken immediately after this sexual activity. A more important question is why are you having sex and not using regular birth control if you are not wanting to get pregnant? Would be best also to discuss with a physician about being on BC pills.