I was talking to a rep (yeah, I know - I always take such conversations with a pinch of salt, but this wasn't directly related to a product), who was saying there is a massive increase in non-seasonal allergic rhinitis in the last few years, and the GPs here back that up. Not clear why this might be, but it seems asthma is more often associated with rhinitis these days, and there is increasing interest in combination allergens where no single cause can be isolated.
The fact that an antihistamine tablet helped would indicate an allergic component.
For relief of a snotty nose, by the way, I find olbas oil, either inhaled directly, or dotted onto clothes or (bottom of) pillowcase helps immensely. I say bottom of the pillowcase, cause it can feel unpleasantly like burning if it touches your face.