Cervical length at 3.0 cms

K

I got to know about my cervical length being on other end of spectrum in my ultrasound at 8weeks, it measured 3.0cms & was again evaluated at my recent ultrasound at 13weeks3days at 3.0 cms only & placenta being posterior.

My doctor has asked me to refrain from having physical relations, should i be worried or consider bed rest?

i’m sceptic as this is my pregnancy after 3 losses.