How soon after unprotected sex can i take a pregnancy test? i took a plan b the same night?

Can or should: It takes time for intercourse to end in sperm finding an egg & more time after that conception to make its way to the womb, implant & make hormones that turn a test positive. A good 10-14 days after exposure would be a reasonable point to test. The tests are more likely false negative if done early, but rarely false positive. From your posted data you have little risk.