Could you have malaria and not be aware of it your entire life?

Sort of: There are several types of malaria, and a couple don't show symptoms that strongly, so mild periodic fevers or lethargy could be pardoned as viral illnesses and ignored. Falciparum, the main kind when people think of malaria, is pretty nasty, causing prolonged and strong fevers, and notable weakness. Generally it gets diagnosed if the facilities are at hand and the history suggests it.

May be: It is possible, however, more than likely the person would have anemia, fever, enlarged liver and spleen and weakness.