How?!?!

After my 5 and a half year struggle with infertility I've decided there's 2 things I really don't understand. 1. I don't understand how it's possible for people to get pregnant just by having sex. Because I've had a doctor insert semen into my uterus via catheter 14 times in 7 cycles this last year and that didn't work!! And 2. How do women not realize they're pregnant? You mean there's really women out there that don't stock up on pregnancy tests and start taking thing starting 5 days before a missed period!