Lost in Pokémon Y!
Likely this means you need to progress with the Team Flare story arc. Go to Lysandre Cafe in Lumiose City. Inside you can enter Team Flare's base. Will avoid saying more since you may not want more spoilers.
Here's a brief video on catching a cab to get there, since you may have forgotten how to get there if it's been a long time since you last played.