My period is late

So I had sex for the first time on nov 9 and it was unprotected and i was scared but my period came 2 days later, but I was still scared for weeks for I got my blood work never showed I was pregnant and I took 2 pregnancy tests they came out negative , but my period is late by one day could it be because i had sex for the first time or could It be i was stressed because I thought I was pregnant