Tell an adult. I can’t tell you what it might be, although you may want to go see an eye doctor. I occasionally had pains like that until I got my glasses. It may be a stress thing too, like getting headaches or migraines but like on the side of your eye. Also, your right eye being bigger than your left shouldn’t be the problem. You either have an eye problem, or you need glasses like I did. Just make sure someone knows.