Early labor? Again?!

I've been very nervous this pregnancy, I went into early labor with my daughter from sex hours before (my doctor told me there's a property in semen that can kick start labor) this was very true for me. 
So this pregnancy it's been on my mind often, I've been experiencing Braxton hicks since 16 weeks, I am now 21 weeks and after my husband cums in me, I notice the contractions are more steady. 
I'm very worried the same thing will happen, my doctor has also expressed concern for repeat preterm delivery and has suggested possible induction to avoid another emergency, but I have this bad feeling I won't make it too far into the third trimester.