I know just how you feel. I suffered losses myself & also needed IVF to get preggo. Trust me, it will get easier to relax as time goes on. I'm currently 26 weeks preggo & loving every second of it.
I also stopped my progesterone at 9 weeks - I was just as terrified as you. My dr actually told me it was okay to stop at 8 weeks, but I had a week left of the prescription & took it until it ran out. Did your dr check your prog level? That might give you some comfort. Anything over 25 is supposedly good...mine was at 35 when they told me I could stop & all has been fine w/ my baby. I know how hard it is to relax...after all it took to get preggo, it's hard to believe something horrible won't happen to take it away. But you're here & this is your time...the time will really fly by, so be sure to try to enjoy the miracle growing inside of you.
Best of luck & many wishes for a healthy pregnancy & baby.