the only way to know earlier would be go see your doctor and ask for blood work.
what if i wanna know sooner? how early can i test?
after you period is missed.. so if you get your period this month and miss next month test then... but if you took plan b good chance you are not pregnant. If you do not want to become pregnant please use a condom and get yourself on birth control. there is no reason to worry yourself everytime you have sex because you are not using anything type of birth control (ex. condom, birth control pill)