It is possible for the period to be delayed if ovulation was delayed, or didn't happen for some reason. This is very common, and happens to most women every now and then. I always recommend repeating the pregnancy test about once per week until the period arrives, but if the tests continue to be negative, the period will probably come eventually. If you were my patient, I would offer you a blood test, and also a 5 day course of progesterone to start you period for you.
I hope this helps!