Has anyone ovulated on schedule , but still had a late period? I am not pregnant, but 11 days late.?

I took 2 HPT's and both were negative. I had been so regular for the last 4 months (like clockwork) so now I'm totally confused. My husband says it could be stress due to the holidays and an out of town trip. I just can't understand why I ovulated, but have not started my period yet. I'm not ready to go to the doctor yet.