Like M3rein said, not all Pokemon have genders. Most legendaries, Unown, Rotom, and a few others lack genders entirely.
That said, it's entirely possible that it is showing your pokemon's gender, just not in the way you expect. I'm assuming you know this by playing the main series games, but Pokemon's genders show up as a single icon - either a circle with a plus sign below it (for female) or a circle with an arrow pointing diagonally away from it (for male).