Can an ultrasound miss Mondor's or HF?

I have some penis pain for a month now and a really swollen superficial vein. I was convinced it was Mondor's and went to the doctor to get an ultrasound. He did it while flaccid (and being worried made me even more flaccid, lol dont laugh) and said the blood flow was fine. Nothing blocked. As soon as I am no longer flaccid however this vein returns and goes from 2/3 up on my penis all the way down to the base where it gets even thicker. It swells even more when sitting.

If it was Mondor's it would be clogged and visible on ultrasound, right?