From all I've read a Mirena shouldn't have any effect on my supply, but since getting it four days ago I've been struggling more and more to produce enough milk for my 3mo and tucked into my freezer stash tonight.
The only things I've done differently recently are get the IUD and increase the frequency of my workouts a bit in the past week. DD hasn't been nursing like she's having a growth spurt, but maybe I'm just oblivious....