Sorry jakek, but whatever it is, it's not an ancient coin. Ancient coins are usually pretty thick and, just like modern coins, almost always are not one-sided unless someone deliberately ground away one of the sides. An object that was made intentionally uniface is usually a purpose-made medallion for jewellery or decorative purposes. This piece has been holed, twice with one of the holes broken, so was presumably considered a memento or good luck charm by someone who wanted to keep it even after the first hole broke.
I can't tell who the portrait is supposed to be; I can't even tell if it's male or female. Perhaps the French emperor Napoleon?
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis