Most likely you are just late since you took a pregnancy test. Those are really accurate. Did you have unprotected sex, by the way? Anyway, periods can be late for a variety of reasons including stress, illness, changes in routine, weight gain or loss, etc. I'd wait a full week and if your period hasn't shown, take another test. Most docs don't want to see you until you've skipped a full month or so. But eventually if your period doesn't come, you can see our doctor. That did happen to me and I had a slow thyroid causing hormonal issues that made me have periods every 3 to 4 months.