A medicinal flavor in beer can be the result of chlorine in the wort from the water or a residual chlorine based cleaner. I am not familiar with Oxyclean's makeup, but from the comments here, I suspect it has a chlorine based chemical in it. Breweries avoid using chlorine cleaners to clean vessels that come into contact with the beer. They generally use caustic, acid and peroxide based cleaners. If you are using tap water and not removing the chlorine by boiling or filtration, this can also cause problems with a medicinal flavor.