how soon can you test for pregnancy?

[princess]

I have heard you shud wait until after your period was due but this does not make logical sense as you may have become pregnant three,two or one week before your period was due. So how many days after unprotected sex will a pregnancy test give you a positive result? Of course the longer you wait the better but I really need to find out asap if I'm pregnant. I heard you can get extra sensitive ones??

 

[Felicia *5/29/10*]

I took a test everyday starting a week before my period was due, sometimes twice a day, and didn't get any positive at all until the day before.