Should I find a new doctor?

So i am 20 weeks along and had my anatomy scan. It showed everything was fine with our baby boy.

However. It showed my cervix went from 3.4cm to 3.1cm. I asked if they can take another scan in a week or so to make sure it's not getting smaller. I had an episode of bad cramping and went to the hospital and they never checked my cervix once, even after I expressed concerns.

My midwifes response was "we dont repeat scans unless you have cramping and bleeding"

Which I feel like would already be too late to do anything, if needed.