Hello Doctor, Me And My Gf Had Unprotected Sex 15

Hello doctor, me and my gf had unprotected sex 15 days before. She was expecting her periods 8 days before but today it's 9 th day till her periods are not happening. Is she pregnant or its may because of stress? We are confused that either we have to go with pills or wait for sometime.
Doctor please suggest what we can do now?
Thank you..!!