Looking for some advice

Hi everyone.  I haven't posted here for quite some time.  I'm currently 24 weeks pregnant and looking for some advice.  Here's the short version of my story. My son was born prematurely at 27 weeks in 2013 for unknown reasons.  This was my first pregnancy, I was 34.  Up until the day he was born my pregnancy was uneventful.  I followed all the rules (eating right, exercise, prenatals, etc.) I woke up in the middle of the night with severe stomach pains, my water broke.  We made it to the hospital and he was born shortly thereafter.  He spent 2 1/2 months in the NICU.  He's now a happy, healthy 4 year old.  Needless to say, having been through such a difficult experience it took some time before we felt ready to try for another baby.  In July 2016 I found out I was pregnant.  I miscarried a couple weeks later.  I had a second miscarriage in November. At this point I was 38. I made an appointment with a reproductive specialist but before the time came, I found out I was pregnant again.  At 12 weeks genetic tests showed that the baby had Trisomy 18.  We lost that pregnancy too.  I rescheduled with the reproductive specialist.  They did several tests and basically told me that my ovarian reserve was extremely low and that it was very unlikely I would be able to have a baby. They suggested egg donation. After about a month of misery I started researching natural remedies for fertility.  I started on several supplements and was looking into acupuncture when I found out I was pregnant yet again.  This time I opted for the more inclusive genetic test.  It came back NEGATIVE!!  I also had a few other tests done and have had several consults with some high risk specialists.  So far everything looks good and the baby is healthy. 

So here's where I need some advice.  I made it through the 1st trimester, and better part of the second alright.  I know it sounds awful, but I tried not think about the pregnancy.  I was so afraid, and still am, of another loss.  At this point, I think I've finally accepted that the baby is healthy.  Now that I'm further along my fear is preterm labor.  I'm taking the McKena shots weekly and see my doctors more often but I can't even begin to relax.  I know there's not much I can do except follow doctors orders and pray but the fear is overwhelming at times.  Coming up on the 27 week mark it has gotten much worse.  How do you cope with it?