Hi!
I usually advise my patients to wait until their period is late before buying pregnancy tests because they are expensive. If you want to test ASAP you can test as early as 4-5 days BEFORE you expect your next period.
By the way, don't forget about emergency contraception (otherwise known as "the morning after pill") if you don't want to be pregnant.
Good luck!
Dr B
UNtil you miss your period