I had Mirena inserted about 3 months ago and have been consistent...

I hate to tell you this since you've spent all that money and are otherwise going okay with Mirena! Regardless of what the scientific literature has to say on the matter, chances are it is the Mirena which is contributing to your weight gain. In my experience it does this in several ways (though I don't profess to understand the mechanisms!). Firstly it seems to contribute to fluid retention and causes significant bloating especially in the abdominal region (pehaps by mucking up your potassium/sodium balance?). Secondly it seems to affect 'normal' muscular development (so, over time, you will probably lose tone and muscle definition, even if you are working at this on a regular basis). Thirdly, it seems to alter the metabolism, perhaps by inducing insulin resistance or something very much like it. The result, for at least some people (even if they don't actually GAIN weight) is that attention to healthy eating, cardio workouts and strengthening programs will do very little. I had my Mirena removed almost month ago and the change is quite remarkable. I lost weight and inches within two weeks, without changing anything. My workouts actually make me feel better, like they used to! I am regaining firmness, particular in my abs/obliques. I have had a period (which wasn't too bad) and I have so much more energy. So, anyway, I can't tell you what will happen for you, but that's my experience. Best of luck!