By pregnancy test do you mean the HPT or the blood test cause the blood test known as Beta HCG is the most reliable. Also sometime it doesn't show right away, if you stll didn;t get your period, wait 1 more week after the last test you've done and do a blood test, if it's still coming negative then it's time to talk to your doctor if he confirms no pregnancy then he can give you treatment to get back your period but that;s up to him, personally I hope you are pregnant!
It is possible that you ovulated later than normal. It is also possible that you did not ovulate at all this cycle and that is the reason for the delay. If it goes on much longer, you need to make an appt with your dr.