Possible Vayne XP Bug

From the last games I've played as Vayne within the month, it seems like I gain less XP than everyone else in the game. And I'm not doing bad in all of them, either. Even when I am marginally ahead of the enemies, my support seems to outlevel me, their bot lane out levels me, our jungler, you get the idea. I'm actually legitimately concerned with if this is a bug or not. It's been quite annoying always being under leveled, even when ahead. If you guys have experienced this too, post a comment or something.