Level/Exp Difference

Is there something I've missed since the most recent patches about leveling/exp? A couple games ago the other team had a gangplank who was fed, and obviously i was assuming he would be a couple levels ahead, but when I checked he was 6 levels ahead! I was 12 and he was 18. The next highest was a 13. I had never had someone over 3 levels ahead in my time of playing LoL. In previous patches I've never seen anyone over maybe 3 levels ahead even when they're 20-0. Or even if I was absolutely fed I would only be a maximum of 3 levels ahead. Also, I've noticed how easy it is to get behind in lane now. I've been on both ends of it, finding myself a much higher level (maybe 2 levels) than my enemy laner even though we're pretty equal in stats (kills, assists, cs, etc). I've had games where I have more kills and more cs but the enemy laner has 1-2 levels on me. Any input on why this is happening? I've only noticed this since the new patches.