Short cervix?

Mb
Has anyone else been told their cervix is short? My doctor discovered it was shorter than normal during the anatomy scan at 21 weeks, I'm now 22.3. Statistically I'm now at a higher risk for a pre-term labor. My doctor said based on my cervix right now she is thinking a 34-36 week delivery. 
She said typically at this point the cervix is around 35mm, mine was 24mm. She limited my activity to no exercise then after an appointment yesterday she limited me even more to minimal walking around for at least a week until I am rechecked. I am taking vaginal progesterone to try and keep the cervix from softening or getting shorter.  
Anyone else having the same issue?