Femara with IUI and trigger shot...first time...

Kristin
Hi all!  I have lean PCOS and My wife and I have been TTC since March. We are finally doing <a href="https://glowing.com/glow-fertility-program">IUI</a> with Femara and a trigger shot after 3 rounds of Clomid (didn't ovulate til the last round of Clomid at 150mg). Switched to Femara and didn't ovulate on 2.5, 5, or 7.5. Now I'm on CD4 and started Femara 7.5. My first u/s looked good today. 
My RE is having me come back on CD 12 to see if im having any response to the Femara. I'm worried that it would be too soon, because in previous months I didn't get an OPK+ (using Clearblue digital) until close to day 20. I feel like my body IS responding and the trigger shot is what I need to get over the hump...but I'm afraid they will think I'm not responding on day 12 if they see nothing at all. Has anyone experienced this?  Looking for a little reassurance. :(