It is most likely plated. " feels lighter than a regular penny." is too subjective. Unless you have trained and had a lot of practice judging weights five grams is about the smallest difference in weight you can detect by had. A LOT of people find plated cents and come online saying they feel lighter than a normal cent, then when they finally actually weigh them they are normal or even a little over. So the first thing you need to do is get an accurate weight, preferably to two decimal places.