I've certainly heard of women not getting a positive result for two weeks after their missed period - one of my good friends is one of those women. She found out with her first that she was pregnant when she was already six weeks along!
If you've been taking at home tests, though, and they're negative, then the chance that you're pregnant isn't super high (but it's not out of the realm of possibility either).
You're doing the best thing by going to the doctor for confirmation. If their test comes back negative, then they can help you troubleshoot why your period hasn't started. That's almost always an easy fix, and it isn't usually a big concern.
I hope you get the answer you want!