I also had an ultrasound during one of those cycles and saw that I was definitely producing follicles. We didn't get pregnant, so now we are onto Femara and
I'm still getting the positive tests and
I just had another ultrasound done to confirm ovulation. So basically, in my case, no one was really sure the cause, but the medication has definitely made a difference and ensured that I am ovulating.
In your case, it could be that your body is taking some time adjusting.