Freaking Out!

I had a MC at 19 weeks in the middle of September. I am now pregnant again 7w 1d. I'm terrified that I will get to that point once again and lose my baby. I have two living children ages 1 & 2 both born preterm at 36 weeks. Drs could find no reason as to why I went into labor at 19 weeks, nor did they know why my two other children were preterm. How do I ease the worry, I think I will be freaking out the entire pregnancy.