HB, I wonder if the body just gets used to a certain level of HRT over a period of time and then it becomes less effective - just as some other meds do.
What is difficult to work out is if the body is going through yet more change - don't they say it's every 7 years the body changes: 0-7, 7-14, 14-21, 21-28, 28-35, 35-42, 42-49, 49-56, 56-63, 63-70, 70-77, 77-84. [42-49, wouldn't want to go through that time again ...]
and the HRT that is/was 'okay' for X amount of years, doesn't cut it anymore.
It is a bummer when you've been on settled regime and then this happens. I hope it stabilises for you or a slight increase remedies things.
Night_Owl
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