k so i got it on wednesday - i'm not going to lie, i hurt REALLY bad. but i don't want to freak you out, i'm really glad i got it now. SO the gyno said it'll be fine, etc mild discomfort etc, but it felt like, the worst pain ever. i was sweating and throwing up and i thought i was going to die. and the majority of that day i was in the hospital at the clinic coz the pain was so bad, but the gyno said mine was a very rare case and that he's never seen it before (even though he's an endo specialist and encourages ALL his patients to get mirena). So this would be VERY unlikely to happen for you, alhtough even if it does, a few days of pain for 5 years of no worry is worth it for me. So hopefully this helps, yes it hurts, and yes it sucks but i dunno, i would definitly still recommend it. Although i'm still a bit turned off the idea of babies if that hurt and people say labor hurts more!
p.s. you can ask for some strong pain relief such as pethidine if you want (if the clinic is nice and empathetic) or anything they are willing to give, i did it with only voltarin and would say something stronger is necessary if you havent had kids.