Pooling of blood can be due to cervical stenosis. Causes of post menopausal bleeding could be ovarian cysts, endometriosis, diseases of pituitary gland, hormonal imbalance of estrogen and progesterone, thyroid hormone imbalance, cervicitis and cervical cancer. Your doctor may consider tests like blood sugar levels, thyroid function test, prolactin, follicle-stimulating hormone (FSA), estrogen, and testosterone. Imaging studies, such as ultrasound, X-ray, and CT scan or MRI brain may also be recommended in certain individuals.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Bug the doctor to order an MRI of your uterus.