Progesterone shots and labor

I'm currently 34 weeks and started progesterone shots around 18 weeks I'll be stopping my shots at 36 weeks. I naturally had my 1st 2 daughters at 37 weeks and my last at 34weeks. I'm already having periodic contractions and I'm wondering when others who've had progesterone shots before had their babies. I'm hoping to go into labor at or around 37 weeks, hopefully not much sooner or much later but I have no experience to go on with the shots