I can well believe that Vitamin D would have an impact - I lived in Corfu, Greece for 7 years, and was probably symptom free for a good 6 of those years! Sadly returning to the UK coincided with a major flare up and sadly no amount of vitamin D can turn back the clock!
I have Remicade, and have had my three loading doses, my next dose is due 30th June. I don't receive fluids afetr (save for the little flush to make sure I get all of the drug!), so I may ask for one if it may relieve the joint pain!