I had sex 17 days ago but was still worried so i took a plan b will the test be accurate now if its negative 17 days later?

Tests are accurate: Today's home pregnancy tests are very accurate and not affected by foods, herbs, common illnesses, sexually transmitted diseases, or medications. A home urine test gives reliable result by 3 weeks after sex (or 3 weeks after when conception might have been) ,or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon.