The Mirena doesn't affect your milk supply. The progesterone in it is such a low dose that it's only localized in the immediate area that it's placed in.
You need to increase your fluids and try eating more foods that help milk production like oatmeal. But you said the baby is nursing more often so she's probably getting enough. Babies are much more efficient at getting milk from the breast than any pump created or than expressing. If she's having a growth spurt that would explain why she's nursing more often so your milk needs time to adjust.
You really have to make sure that you're getting enough rest, that you're drinking enough, and eating enough. Pumping is not accurate as to how much milk you're producing since a baby will always get more from you than the pump.