Call your doc and set up an appt. I was 11 days late and if I was still testing negative and no AF by the end of this week, my doc wanted me in. Better to play it safe!
I's not likely. Sounds more like just a fluke in your cycle. You can try tracking your BBT to see if you are ovulating. I went 64 days without a period a couple years ago, I went to my doc and that's the first thing he told me to do.
HPT are pretty accurate and based on your symptoms it doesn't sound like you are. :-( Your body might just be having a crazy cycle this month and it's lasting longer than usual. Call you doctor and set up an appointment to find out what's going on.