Not dilated but could feel babies head?! How?!

I am 33+1. I am one of those that has been contracting a lot and been admitted to the hospital but no change in cervix, so they can't do anything. Well today, I had an NST and cervix check. The nurse practioner did the cervix check. My cervix is soft, maybe a finger tip, and she could feel babies head. So she said my cervix is probably not 4cm like it was last week via ultrasound. But then my doctor came in and said there is no real way of knowing how long the cervix is without an ultrasound and you can always feel babies head. Really? I thought you could only feel the head when baby is dropping? I'm confused.