tkdesign,
usually we take calcium with Tymlos and Forteo and vitamin D3. D levels often drop because PTH uses it effectively to increase absorption from the digestive tract.
The low urine calcium could be that already elevated PTH is pulling calcium back from the kidneys before it can get to the bladder.
You are a bit of a mystery because of consistently high PTH may have contributed to your bone loss. How high might yield a better clue. I would want an ionized serum calcium
level to help understand.
I would take the md's advice about calcium and take D with frequent labs to see if the parathyroid gland is just adequately responding to low calcium availability.
Are you using bone markers.