people who get pregnant on accident

How does this even happen?  I've been trying with my husband for a while now and I get so frustrated when someone tells me it just happened.  Or they weren't even trying?!  I have a job where I deal with people regularly and they ask often when will I have a baby.  I chose to not tell anyone but my best friend I have been trying because I work with a bunch of women who will say i can't believe you're not pregnant yet or things like that.  I am ovulating and have normal periods but geez I thought getting pregnant was easy.  Seems like for most people it is a lot of work!  I hate having this why can't that be me attitude toward pregnancy but I can't help it.