Could I be pregnant?

Usually I get my period around the 15th but November 15 comes and goes and I didn’t get it. So I waited thinking it’s probably just late but now it is December 1st and I still haven’t gotten it. So got a clear blue test and took the digital one. “Not pregnant” popped up on the screen but it still makes no sense. How can I not be pregnant but also missed my period the entire month?? I still have the regular test that I will take in three days to make sure but has that happened to anyone else? You took a test that said negative but you missed an entire period, and if so did you take another and it came back positive?