Hi Holidaygirl
from me too.
Sorry to hear about your problems. However I am surprised that your doc put you onj tablet hRT when starting for the first time over the age of 60 as transdermal is normally recommended due to increased overall stroke risk with age and potential slight risk with oral HRT. However I presume you are very low risk generally eg fit and healthy with plenty of exercise, good diet and normal BMI, no smoking, low alcohol etc?
It sounds like your womb lining may well have built up - either post-menopause ( as some ovarian activiy continues even if no ovulation, or possibly you have a fibroid or something - which might have been one of the causes of your previous heavy bleeding? Did you ever get this checked out especially due to your late menopause?
Anyway provided all is normal you will still be able to continue with hRT but perhpas in your position why not ask for another Mirena if that suited you before? Then you can take oestrogen ( patch or gel) at a dose that eliminates your symptoms and will stop any bleeding - once any lining etc has shed? Now you are post-menopause the bleeding should stop with the Mirena if all is otherwise well.
Please do not give up hope - your quality of life can still be improved by using something different. However if you do want to continue I would ask GP to refer you for scan just to make sure all is well and then maybe think about these alternatives?
Hope this helps
Hurdity x