How many times can you use letrozole to conceive?

Hello! I have PCOS- had a horrible journey TTC to get my diagnosis- and now two successful pregnancies using provera to induce a period and letrozole to make me ovulate. My son is 14 months old and I am currently 13 weeks pregnant with baby number two. My period never returned after my son… so at 12 months we started the fertility drugs again. I am curious, how many of you had to use letrozole to conceive more than once and if so is there a limit to the number of times you can use it? I’m really hoping for 3 beautiful children in my life and sometimes it’s hard to come to grips with the fact that my body seriously just doesn’t want to reproduce naturally.