They left you with one parathyroid, right?
Have they checked your Vitamin D? I found this:
Secondary hyperparathyroidism is usually due to kidney failure. In people with kidney disease and/or failure, phosphorus may not be excreted efficiently, disrupting its balance with calcium. Kidney disease may also make those affected unable to produce the active form of vitamin D, and this in turn means that they are unable to absorb calcium properly from the diet. As phosphorus levels build up and calcium levels fall, PTH is secreted.
More info here:
http://labtestsonline.org/understanding/analytes/pth/tab/testI hope they get you straightened out Neo!