I had a scare once where I thought I might be pregnant- it was terrible. Eventually I did get my period. Remember that stress can make your period late- so perhaps you are making it worse? I think that's what happened to me.

However, some tests work better at different times- some are early detectors and some you need to take a week after your missed period, I think. I would say to get an early detection test and see how it comes up, and to relax. It is possible that you're pregnant, but it's also possible that your period is just late.

Good luck.