Letrozole (femara) still no ovulation

So I started my first cycle of letrozole. I took the 5mg as directed cycle days 3-7. Started testing cycle day 10. Still havnt gotten a positive, not even close. It seemed like my test strips were starting to get darker, then they got lighter. But never got a positive. I’m on cycle day 16. 😞 is it possible to ovulate late while on letrozole, or did it not happen? Worried I’m never going to ovulate. Did anyone have a similar situation?

Looks like it was starting to show the second line...then it never got darker to get a positive. Now it looks non existent.