Could Having Unprotected Anal Sex Cause HIV Infection?

Hi doctor,
I have been into unprotected anal just a week ago and feeling low because of it... there's a constant sprain in my mind whether i had contracted hiv because of it... so please advice me where and what test should i take to know whether i got infected or not... all over the internet there are thousands of articles ...some say the tests are accurate and some say these may be false positive... am confused... so please advice me doctor.
Thank you very much
Regards,
ARSLAAN