Cervix length less then 1cm at 18 weeks pregnant!

I’m only 18+2 weeks pregnant and I’ve been bleeding the last 6 days. I was in the hospital for the 4th time this week to find out the reason for the bleeding. The doctor checked my cervical length and said it was .6 cm and it should be at least 3.5 cm. She wants to start me on progesterone on Friday I’m not sure why not sooner but it is supposed to help my cervix stop shortening. I’m thankfully not dilated but this is still very scary. She said my body is going into preterm labor. I’m currently on bed rest and praying for my baby boy. He will be my first child. Anyone have something similar happen and it turned out ok?