I have been sexually active for about 3 months now. Usually before sex, my partner and I have a few minutes of unprotected sex and then he puts a condom on. My period is now a week late and I'm worried. I already took a test that came out negative but I'm still kinda scared. My friend told me that it's usual for my period to not come when first having sex. Is this true or should I wait a little while and retake a test?