It is not uncommon at all for postmenopausal ovaries to randomly chuck out a last egg in the first few years after menopause.
The premenstrual type feelings such as breast tenderness, plus the recent negative ultrasound, all point to a benign cause.
I really, really wish there was less fear around bleeding - even for women not on hormone therapy it turns out to be cancer in far less than 1% of cases.
Whilst it does need to be checked out, I really wouldn't lose any sleep over it.
