Follicle size/growth on Letrozole

I am on my first cycle of Letrozole this month (TTC #1, PCOS), and had an ultrasound yesterday (CD12) to measure follicle size. I have one follicle on each side that each measure 12mm. The doctor said that they were too small for her to give me the trigger shot, but to use an opk at home, and if I don't get a positive on that by Saturday to come back in for another ultrasound and the trigger shot a s long as the follicles have continued to grow to at least 18mm.

Does anyone have experience with this? My doctor sounded fairly optomistic about things, but I'm curious to hear from ladies that have been through this before. Did your follicles continue to grow? Is it common not to get the trigger shot at the CD12 ultrasound?

We have been TTC almost 2 years, and I went through several rounds of Clomid last year to no effect. I didn't ovulate with Clomid at all.

Any advice is so appreciated - thank you! ❤

EDIT: Forgot to mention that we are doing Letrozole/Trigger Shot/Timed Intercourse this cycle, but will pursue IUI on the next if this isn't successful.