I have a few thoughts.
While hormones are all over the place post partum, this has been going on too long.
The hormone in Mirena is a progestin, a synthetic version of progesterone. It does not offer some of the benefits of progesterone (because it is not) and also can have some unhealthy side effects. Progesterone is important for quality sleep and its calming effects. She could be tired because she is not sleeping, low libido and motivation also because she is tired. We have the women take their progesterone right before going to bed. It is great for promoting good sleep.
I wouldn’t give up on thyroid. Sure, number are numbers, but what about her symptoms? I’ve placed women on thyroid with these numbers. To cloud the issue, many low thyroid symptoms cross over with symptoms due to other hormones.
Low thyroid patients will get a good nights sleep and wake up tired, but she probably does not get a good nights sleep so this cannot be used for determination. They always feel like a nap. Thinning hair, eye brows, dry skin, brittle nails. They carry some fat that seems impossible to lose. Of course, they feel tired all the time.
She could try melatonin.
Testosterone could help with her libido. Her free testosterone is around 1%, which is low. Test would also help with her energy levels, strength and lean muscle.
She could be looking at several options. To begin, I would stop Mirena. I encourage every patient to do this. Yes, you’re looking at another form of contraception, however, synthetic hormones are not healthy.
Good luck, I know this is very frustrating.