It's great to find someone else with this same side effect. I have had the mirena for 3 and a half years also. In the past 6 months I have started producing colostrum. I breastfed two kids (5 and ahalf years ago, and three and a half years ago) each for about 9 months. Also I NEVER found it easy to get the feeding started after the birth, and colostrum was hard to get any. Now I have plenty. I'm not pregnant.
So I'm assuming it's something to do with the Mirena. The only other things that have changed for me are that I've been taking atrovastatin, and blood thinners.
I want to get rid of the Mirena and see what happens.