If the oestrogen is measured in pmol/l then this is quite low whenever it was taken although levels do vary considerably.
What reason was the doc doing these blood tests?
If you are over 45 and getting menopause symptoms such as flushes and sweats then you are peri-menopausal. With the Mirena you don't have cyclical changes to tell you although blood tests can tell you a limited amount.
Hurdity x