what should i do?

okay so I regularly have protected sex (condom) with my boyfriend. we've never had a condom break or anything but my latest period hasn't come yet and its and entire week late. I've taken a pregnancy test but the test reads negative. I plan on taking another test later this week but honestly I'm confused because of how late it is, I'm only 15 so maybe it could be because I'm young or something but this has never happened before. have any advice?