What Causes Spotting With No Regular Menstrual Period?

Hi I have a question about "Teen Pregnancy"... I want to know if I'm pregnant or not...it seems a bit early...but I haven't had my period for 9 days, and this afternoon I think it came, but it's so little, it's like a couple of drops and it's light (plus my nose bled a little..like one drop or something) I'm just confused because I haven't had protected sex, but then my boyfriend never spermed inside me either. So how is it possible, or is it possible that I'm pregnant. And also, I don't want to do a home pregnancy test yet, because I think it's still too early?