You can test 14 days after unprotected intercourse - you do not need to wait until your next period is due unless you have a perfect 28 day cycle and have sex on day 14.
Oh you can take a test when your period is due.
Anytime you have unprotected sex you run the risk of becoming pregnant or getting an STD.
6-7 days after your last period ended is the perfect time to conceive. Sperm can live for up to 5 days in the vagina.