How soon can I take a pregnancy test

I had regular unprotected intercourse a week before my period was due. My period did not start and I have no signs of it starting (I usually get cramps and tender breasts). I took a test a day after my missed period but it was negative. I am thinking that if I did conceive a week before my period then maybe it was too soon to test? Could pregnancy be the cause of a missed period 1 week after concieving or would it be too soon for my period not to start? Any advice would be great.

[Kimberlee_20]

A woman with a normal menstrual cycle ovulates two weeks after her period, you had unprotected sex 3 weeks after your menstrual cycle (if it was a week before your period was due) so it's unlikely you had sex on your ovulation days. If you were pregnant, your period wouldn't start, even if it was just a week before your period. You can test 3-4 weeks after unprotected sex and get an accurate result, if it's negative then you're probably not pregnant and you should contact your OB/GYN and ask them why your period isn't occuring. Good luck!