Switching days

Getting ready for my 4th iui

Previously we did 2.5 mg Letrozole

for two cycles and last time 7.5 mg on CD 5-9. I did try clomid my first time but ovulated too early so we couldn't get iui done that month. Second time on clomid iui failed and thinned lining

This time we are doing days 3-7. Has anyone had success switching days? We will be triggering as well. I was told last time that i didn't need to use opks because of triggering. But i can't help but think that something timing wise isn't adding up as it hasn't taken yet. All tests have come back clear and donor has been switched. I ovulate on my own. Long story short.... success on switching days of cycle and should I still test using opks even though i will be triggering. Hope that all makes sense! Thank you.