Why not take a combination estrogen/progesterone birth control pill without taking any breaks, for a good several months, and then stop to see if Mirena has kicked in at last? The amount of progesterone in Mirena is low, so I doubt that combined, mirena and the pill will cause an OD of progesterone.

How cruel of nurses to ask you if you were excited! Had you been excited, it would have been written all over your face... psych nurses should read faces better than anybody else.