A few years back I had problems with serial colds. I think it was a side effect of some medication I had recently started taking (Advair).

But I also realized that my diet was probably low in iron and zinc, which might have been affecting my immune system, so I started taking a multivitamin every day. I can't swallow giant pills so I take Centrum chewables. Since then I have only gotten one or two colds per year.

I also used to try to keep up my exercise routine while I was sick, but now I take a few days off as soon as I start to feel sick and I take it easy until I'm feeling better. It's hard getting back into the swing of things afterwards but I definitely get over the cold faster.