23dpo, 9 days late and BFNs

Hello all, please help me.i am 23dpo , late by 9 days( which never happened before in my lifetime, AF works like a clock). I used opk to predict my ovulation day and I did get a positive opk test on April 19th. I have been having cramps on and off but no period and now I am shy of having my AF next cycle by 18 days.whats happening ?

Any experiences that are similar to mine, and got BFP.

Thanks