Beata... I'm on my first cycle post stim cycle. Stim cycle AF was on time, but this month I am already a week late with 2x neg hpt's. In my case it seems the stim cycle has really messed me up, I haven't been more than 31 days in 3 years so this is really pestering me too.
So I can completely understand your frustration.

Hopefully my IVF clinic will call me back tomorrow (that's when my fave nurse is in) so I can find out what's happening.

Hang in there because I am right there with you. (Going nuts).