20 days late!! And TTC

Britney • *27* Married, Jesus Freak! Mother of Bella Bliss 👶🏽💜🎀 TTC baby #2
I was 20 days late of my AF but it finally decided to join me yesterday... I took two test and they were both negative... Why did this happen? And what could this mean? I have a doctors appointment on the 17th I need answers! Does this mean my ovulation is going to be off or different? Help!!!