Getting pregnant again

So, my fiance wants to try for a baby but I'm scared like I don't even know where to start. I have a son already which is 3(isn't his), and my birth was traumatic .. Now that he talks about having one, I avoid the conversation. I get anxious and I do suffer from panic attacks. I'm hypochondriac as well, lord I just can't think about having another baby knowing what can possibly go wrong. I'm so careful when we have sex, I make him wear condoms. I recently got diagnose with pcos, so no I still wouldn't have unprotected sex. Idk how can I get over it, I be overthinking. yes I'm that one women who gets happy when AF arrives.. This sucks cause he looks at other babies and I can see the sad faces he makes. He knows everything about me so he understands and is very supportive.