I am trying to figure out why is it that I always gets allergy and blocked nose during the change of season time in Canada. What I mean by change of season is when the weather starts to become colder, during the months of October to November. It also happens when the weather starts to get warmer during the months of April to May. Is it the flowers pollen or dust or something causing such allergy. My Doctors haven't been able to pinpoint my allergy problem and I passed all the allergy test though.