Hia Arson,
Can you give us a bit more info, flesh out the bones a bit. What dosage HRT are you taking, is it keeping your other meno symptoms at bay?
Are you having hot flushes? Apparently, brain blood flow is reduced during the menopausal hot flushes, so it's not unusual to go blank at these times.
Are you taking Testosterone also? Both hormones are said to help with cognitive function.
TD