This will be long, but looking for support

Ok long story so bare with me. I have 2 children already. A 5 year old son and a (almost) 3 year old daughter. I had my first MC right before I became pregnant with my daughter. So my children come from my previous marriage. I should have left sooner, but kept trying because of my son. My ex and I literally had sex ONE time when I got pregnant with my daughter. Faat forward a bit, I divorced my ex when my daughter just turned one. So ok now with my current fiancé. He has no children and is an amazing father to my children. He has always wanted to be a dad. We had a missed mc in January fallowed by another mc the next month. I have been tested for hashimotos and phospholipids and both came back fine. We haven’t taken the next step in genetics yet. But I am just so broken feeling. I kept help but to think about my daughter (I love her so much and wouldn’t change a thing). But WHY could I get pregnant with sex the one time and sex I didn’t really want to have, but I can’t get pregnant now that it is SO wanted. Does that make sense? I just feel like broken. I just don’t get why it was so easy before and now I either loose the baby or can’t get pregnant. There aren’t really people in my life I can talk to about this, anyone that would understand anyway. I just got the OK from my fiancé to buy ovulation trackers and fertility supplements.