How soon after unprotected sex can I know if I am pregnant?

I have the Mirena IUD. My period isn't normal, I spot/bleed for couple of days and it goes away. I don't know when my period would start or end since I constantly spot and bleed. I had unprotected sex but im afraid of becoming pregnant. Does anyone know when I can take a pregnancy test?How soon after unprotected sex can I know if I am pregnant?2-3 weeks After unprotected sex...sperm can live in you for a few days so by about 3 weeks after sex u should get a reliable result. If you on using mirena though I'd say its highly unlikely you are pregnant. Contraception is always making periods weird so I wouldn't worry...see a doctor if you're worried though or look on the internet for mirena side effects to see if that's normalHow soon after unprotected sex can I know if I am pregnant?If you are scared of becoming pregnant than don't have unprotected sex.. As matter a fact, don't have sex at all because the condom can always break. Common sense, hun.How soon after unprotected sex can I know if I am pregnant?about 2 weeks after u ovulate