Hi pricey
Sorry to hear about your symptoms. I don't really know what to suggest. If you have continuing breast pain without having changed anything else maybe a trip to the doc would be in order, just to get checked out. Usually if caused by HRT this would settle and if you haven't changed anything, would be less likely.
There are women who do continue to ovulate at your age though. Do you definitely know you are post-menopausal ie very late peri or post-meno when you started HRT? if you were only early peri-menopausal 5 years ago there is a possibility your natural cycle is still happening.
I understand your feelings about not wanting to change things but if you're not feeling good you probably need to do some tweaking yes. Another alternative is to go to a longer cycle and see how that works for you, depending how much bleeding you are getting with 12 days x 100 mg Utrogestan on a 28 day cycle. You might need to increase the dose of utrogestan in this case but does depend on your womb, and also needs to be done in consultation with your doc to make sure you don't get a build up of lining.
Sorry I can't be any more help
Hurdity x