Hi kiltgirl.
If I were you, I would get the Mirena removed asap and see how you feel. I am very sensitive to progesterone (most women who suffer with PMS are) and when I tried the Mirena it gave me much worse PMS, and I had it ALL month.
Just because the progesterone in the Mirena is released locally, it doesn't mean it STAYS locally. It can, and does, travel around your system and it can cause dreadful symptoms in some women.
Prof Studd mentions on his website that in some women the Mirena can exacerbate their PMS, and he doesn't recommend it.
I am one of his patients (my PMS has been getting steadily worse, until it became PMDD, and then got even worse in peri Menopause), and one of the first things he checked was if I had the Mirena, because if I had, he would have wanted to remove it there and then.
I am currently on a combination of 4 pumps oestrogel + testim gel + 100mg Sertraline and it is certainly helping - but my PMS still comes back every month. It is dreadful. I am crippled with anxiety and have felt suicidal at times. The depression is soul destroying. Then it suddenly all disappears as quickly as it came.
Prof Studd has written to my GP recommending I try a course of Zoladex injections + add back Livial. And I'm just summoning the courage to try it.