I just dont get it!

I'm so heart broken and upset. Im 3 days late for AF, 16 dpo and still getting BFN. My cycles are clockwork- 28 days from CD1 to CD1. But not this month. My temperature dropped this morning but is still well above the coverline.

I dont know what to think anymore. I have an appointment with a fertility specialist Friday but I dont even know if I should keep it or not. If I don't get AF and I'm still getting BFN. I'm not sure what to do.

Any idea? Has anyone has similar situation and ended up with a super late BFP?