you are right, if you have not had a PTH level, this is required. If it is >40 (with upper normal of 65), then this is primary hyperparathyroidism.
HCTZ (the med the endo likely had in mind to 'absorb the Ca) is not the right step in these cases as it will further increase blood Ca.
parathyroid and calcium - are connected. have a thyroid pannel test done too to see if you are also hypothyroid. check for TSH, (should be below 2), T4, T3, FreeT4, FreeT3 and thyroid antibodies TPO to see if you have also thyroid problems. I wish you good luck and even better health!