Delayed ovulation..causes?

I do bbt & opks so I know I am not close to ov, & I’m cd 16. I ov 48 hours after first positive opk & still haven’t gotten a positive. I also don’t have ewcm yet, & usually start getting that around cd 8-10.

I took letrozole 2.5 mg cd 4-6... is that causing my delayed ov? What could it be??

Also... do you think it will even work now? It’s so late. I feel like if it helped, I would ov on time if not sooner & a really big follicle. 😞 Ugh..