I also wanted the injection because of the 'embarassment factor' (Had Cesaerean, so didn't get any peering down there.)
But, was talked into the Mirena , because of my age and with me comming up to the menopause - I'm 36!!! I also don't want anymore children.
The fitting is not that bad - you lie on your side so they can't see your face and you can't see theirs, which helps.
I was advised to take a couple of painkillers an hour before. It was fine, I was really dreading it, it was uncomfortable but nothing like what I was fearing.
I bled for a couple of weeks after (normal) and that was that. I've had a few spots since and Hey presto.
I'd recommend it, sorry no help with the injection info though.