Is it nerves? Or pregnancy?

Okay so.. my boyfriend and i had unprotected sex (yeah I know, it's a bad thing). But he never ejeculated inside of me (wow i feel weird saying that lol). Well anyway, this has been going on for about two weeks now. I bleed a little, but not even enough to cover a tampon or anything. And it's all brown like it could be dry blood. I dont know. My mother insists on me taking a pregnancy test, but I just started my senior year of highschool last week. Do you think it might me nerves or stress? Or could I actually be pregnant?