I had this cold that lingered for three months. I tried using OTC remedies, with little effect, but not oil of oregano. I noticed that my body temperature was actually lower than normal, yet I was feeling feverish most of the time. I went to the YMCA, where they have both a steam and a dry sauna, and was in that for most of about 8 hours. Next day, the cold was gone.

I realized whatever I had wouldn't let my body temperature rise up to fever levels. So, I sought an external way of doing it.