I would recommend you get a second opinion from an oncologist. I would take ALL of your films, not just the most recent, and go to a hospital in the "big city" or one that specializes in cancer treatment. If you are at what some of us term "dirt and sand" areas, you really need a fresh opinion from a specialist/ preferably an oncologist. Also, try to have your x-rays done at the same facility, and if you can't make sure that the doctors (radiologists and your current doctor have compared all of your films.)
I worked for a medical malpractice insurer for many years, and you have to walk a delicate line between being a PITA and assertively involved in your own care, but its your life.
NEVER assume, doctors or radiologists are on top of things. It is extremely difficult to be. You must be on top of making sure everyone is getting and reviewing the films and reports.
But seriously, it could be a lot of things. What are your blood tests coming back as? Anything weird there? Also, again, don't be too paranoid, but look at your family history and get the other areas tested. If you are a smoker, then getting a CT of your chest is a no brainer.
Good luck-- If you are in the PA/NJ/NY area I can definitely recommend someone specific.