Hi Tc, I don't have any experience with the Mirena so I can't give advice about that but I did have a birthcontrol containing Levonorgestrel and at first it made me depressed too. After about six weeks those feelings and other side-effects subsided and I felt fine. If these side-effects started when you decreased the Sandrena it could be the pellet hasn't kicked in yet as you say, as the estrogen counteracts the progesterone. Did they give you any indication how long it would take for the pellet to work fully?
I do have leg pains but no Mirena,. For me it feels like my trousers are way too tight , even if I don't wear any, and something is oppressing the veins in my legs. Restless legs too.
Alicess X