Just want to add that Vit D didn't do anything for me. Took 100 000 IU's per week in two doses for two months, as prescribed by an endocrinologist after blood tests showed I was low. I could as well have taken smarties..no effect on symptoms. I didn't even bother to retest after two months. Vit D didn't cause my illness, and looks like it won't cure me either.
I live in the southern hemisphere and although it's "only" my second year with this illness, I'm also feeling a definite increase in severity of symptoms now that it's getting colder and the seasons are changing. Even before getting this chronic illness I had a problem with respiratory illnesses during the switch from late summer to autumn. I'd always be the first one in school to get sick, but then I'd be fine for the rest of the winter.
Seasonal relapses with this illness could be down to a number of factors like increased viral and bacterial load, temp and pressure changes, increased pollution (greenhouse effect is more pronounced in winter, at least where I live) etc. which all places more stress on an already battered body.
Best of luck for everyone who might experience this. Hopefully this winter will bring good news in the form of new research so we can focus on something positive for a change.