Are you regular? Because for the first few years of me having one, it came and went as it pleased. I'd be late all the time.
It could also be due to stress, change in diet, changes in your emotional well being...
It could also be due to medical issues. If you think its serious, you could always talk to your doctor.
As far as pregnancy... have you had unprotected sex recently? Because even if you are two weeks late, you wouldn't be able to "just notice." I was over two months pregnant before I finally tested and got a positive. I had absolutely no symptoms until well into my pregnancy to let me know.
Hope I helped!
PM me is you have any more questions!