You can test that early but this is my fourth pregnancy and I've never had any luck even a day before my period is due.
waiting another day seems too long! ha, i'll try to wait. i've heard you can take a pregnancy test 5 days before your missed period? my period is supposed to start nov.6 i believe, so could i take one 5 days before that?
If you haven't gotten a period 18 DPO then test.
I would wait 2 weeks from when you had unprotected sex.