Letrozole help

So on day 3 of my cycle I started my first round of letrozole but when I did my scan at the RE on day 12, I had a bunch of follicles that were under 10 so we didn't do IUI. The RE upped my dosage for the upcoming cycle because he thinks that 2.5 wasn't enough and that's why there wasn't any mature follicles. Well, it is cycle day 37 now and AF won't show her face 😕 and I have only had one occurrence of a very light spotting of old blood. Has this happened to anyone with letrozole? My cycles are regular so I'm pretty sure it's the medication throwing things off.