I'm not sure about
the headaches/ sinus issues as that can be caused from so many different things. The obvious one is local pollen. I have found this neat site where by entering your zip code you can get a detailed listing of what's creating pollen in your area!
www.pollenlibrary.com/ It's a place to start!
For the elevated PTH levels, have you had your blood calcium levels checked? These often respond in tandem, since the parathyroid gland regulated blood calcium levels.