Officially on watch for Preterm Labor :'( Advice

Last Friday my stomach started getting super rock hard accompanied with huge amounts of pelvic pressure, lower back pain and abdominal cramps. I have been to Labor & Delivery Triage 4x since then for monitoring and to make sure im not going into labor.

Im only 24 weeks.

I finally saw my OB today who has bumped my appts to every 2wks now and wants to do ultrasounds to keep an eye on my cervical length. Right now im @ a 3.2. He says if it gets to 2, were in deep shit. Hes also informed me that this is typically how preterm labor starts. But right now, I'm not having enough contractions to make any changes or start dialating. So that's excellent news. And even better if it stays that way.

Im a healthy 30 yr old who could may be better her diet but thats about it. I was so confused as to why im suddenly a preterm labor risk. Then I realized that a "second term 'abortion'" increases your risk. I technically had to have a "late term abortion" with my last pregnancy when I lost my daughter at 19 weeks. A D&E to be exact. This is my rainbow baby. My son and last pregnancy. Dh and I are scared and nervous. I'm wondering if anyone has had any experience with this (preterm labor) and if it's pretty much guaranteed to happen? Help and prayers please ladies.