Could Doxycycline Be The Standard Treatment For Reiter's Syndrome?

I have recently been diagnosed with Psoratic arthritis, and possibly Reiters Syndrome. I have been given doxycycline long term. 100 mg for approximately 3 to 9 months. Is this a standard treatment for Reiters? I am plagued with stiff sullen joints. Blood tests indicate Psoratic athritis and Dr suspects Reiters? Appreciate your thoughts!