Hi debini2874, welcome and thanks for your question.  Your Dr. is absolutely on the right track in sending you for an evaluation from an Endocrinologist.  When we don't respond to these meds there could be many reasons, but one of them is that there may be a secondary cause for you bone loss that needs to be treated seperately.  Low vitamin D levels, low calcium, or loosing calcium in urine are, along with thyroid, and parathyroid disorders are just a few things that can cause bone loss.  Here's a longer list of secondary disorders from the National Osteoporosis Foundation that you can read and see if any of these things apply to you.  The link doesn't provide a complete list of things that cause bone loss so do some reading on "secondary causes of osteoporosis."  While at the above link also check out the "medications" that can cause bone loss to see if you are taking any of those, and you can find those just above the area on disorders that cause bone loss (scroll up).

Good luck and I hope you find out what is causing this problem and keep us posted if you don't mind