You do not give your son's age which is vital here in order to answer your question. Very young children under 3 years do not have sinuses as such except for very small pea size sinuses on either side of the nose. I don't think this is the problem. The problem does not sound like asthma either or croup. The most likely diagnosis with your story of the illness only being present in winter is that of recurrent viral wheezing. He will outgrow this illness by the time that he reaches primary school going age. The treatment is the same as for asthma, that is why he benefits from the asthma treatment.
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