Getting the flu is the worst. Have you tried ending your shower with a minute of cold water only? I got into that practise in Russia/Finland (they call it contrasting temperatures). I used to roll in the snow, or pour rainwater over my head, while having a sauna. Sounds crazy but no more colds, not one. I get the slightest touch, see my work colleagues dropping like flies but the next morning I'm fine. I cycled through weeks of rain this winter and I don't have a waterproof jacket, still no colds.
At first it will feel cold but then after a few months it will feel refreshing...promise