OPK went from dark to light 🤔

I started taking letrozole aka Fermara on cd 3-7 and my cycles are anyway from 28-33.

So, I started testing on cd 10 per my RE and test were getting darker but not dark enough for a positive. Well, cd 15(yesterday) the line is super faint to the point where you can’t see it. I don’t see how I could have missed it as I’ve been testing 3-4 sometimes 5 times a day just to make sure I don’t miss it because Ill need to schedule my

IUI

after getting a positive opk for the following day. Last month I didn’t get the opportunity to do the

IUI

because of my husbands low sperm mobility and now this 😢 I must say our first

IUI

was successful and DH swimmers were great...

Also, I ovulate on my own so maybe the letrozole didn’t work and my body is waiting for me to ovulate on my own....🤷🏽‍♀️

(Currently on CD 17 & negative opk)