Hi all, thanks for the answers so far.
I called my aviation physician and explained to him the case. He also told me that "old" antihistamines used the be an issue, not so much with the newer ones.
We discussed the details; I've been taking this specific brand for two years with no negative side effects. I feel fine both driving and flying (flew with it last season unaware it was against out ops manual). However he was unsure of how the legalities are working out (I asked if there was, or needed to be some kind of medical release), so I sent him an email for him to forward to his superiors at the regulator, so we'll see what they say.
I also directed the question to my company, they replied that the text has been unchanged for years. It also include a vaguely worded sentance about red warning triangles on the affected drugs, however that, as I see, does not void or limit the first sentance in the paragraph, saying explicitly that flying on antihistamines is prohibited. (Not "antihistamines marked with red triangle").
So for me it's not really a practical problem as it is a legal issue. Personally I know that said medication works fine for me, but I don't want to knowingly disregard the ops manual every time i fly, I want to do things right (ie get any liability off my back). Right now, not a problem, as I'm off it, but I need to start taking it within a month, max two.
Furthermore, this is applicable to multi pilot operations, and watering palate is not practical as we do not have a toilet onboard. I also did a search on these forums for "antihistamine" but there were no results.