The hormone in the Mirena can raise bloodsugars, and there is such a thing as the "Mirena Crash", which you described, after removal. And in some people the Mirena actually ended up causing T2. So yeah, it could be that you'll get better bloodsugar control now. I get a Depo Provera jab myself every few months because Mirena and I didn't get on well. (Small womb, I had contractions for half a year before we figured out what was causing the pain). The shots have their own side effects, but for me, it's the only way to have some control over the migraines. I was always sturdy, but when I got the Mirena the first time (I had three until the last one sent me to hospital), I gained a lot of weight in 3 months. And every time I changed it, I gained some more. Add a not very helpful dietician to that... It did not go well.
So... Have had shots now for years instead. And in the meantime got my diabetes T2 diagnosis, started low carbing... The weight's not entirely gone, but I'm not morbidly obese anymore, so yay. And good on you for testing, because how else are you going to know what's going on eh?
As for eating healthily, I hope you know that for a T2 that means something entirely different than the common advice? You might be able to avoid T2 meds entirely. As for getting the shakes at 4.3, that's a false hypo. It feels like a hypo because your body thinks that it is, because it's used to you having higher levels. So it freaks out the way it would if you were. It'll get used to normal numbers soon!
In any case... Hope this helps!
Jo