4 days late negative tests

Posted in another group but realized it was not really the right place to post.

I am 4 days late for my period (normally I am extremely regular and have been on time / early for every period for the last 3 years).

I had mucus changes and confirmed ovulation with blood work and urine strips (I am currently waiting to start treatments for IUI) so things are being closely monitored.

Has anyone ever experienced this?

I am anxiously waiting my period so we can begin fertility treatments after trying to convince for 2+ years.

Advice and anything else is 100% welcomed.

Thank you in advance !