its the oil pump mate definately, as the oil light comes on at 5 psi of oil pressure and the sensor for oil pressure is more or less directly next to the oil pump output so there is no chance for the engine to loose the oil pressure,

you need to replace your oil pump and also check you havent caused any damage
but when the oil light has come on it is usually too late anyhow

how many miles has it done on that oil pump?