There was a item in the paper (can't remember which paper - sorry!) a few weeks ago about an American plant that doesn't usually grow well in the this country because the early-autumn chill kills it off before it can flower ... but this year it has been able to flower very well and its pollen has been found in places it's never been found before. The article said the pollen is a powerful allergen, so hay-fever symptoms were likely to appear unseasonably late this year - this could be your explanation?