Faint line ?

So is any faint line the start of something, I'm 10dpo and I can see the start of a + sign, it is faint but it is there. Expected period is Thursday 2/12/15 and me and my SO had sex every day except one (2nd day in) to my fertile window. Is their a good change that + sign can darken?! This is #3 for me and with my other pregnancies I have never had major symptoms, so that is nothing new but I've always had strong lines, maybe I just tested too soon than before but any input is helpful! Thanks ladies!