Is it just me or is something off about EXP?

As someone who likes to roam a bit as support just to ward and back up other lanes, I've recently begun to notice that I'd start getting really behind in levels. Normally, I'll be down a level or two, which is normal, but I remember vividly for 2 games I was down the enemy midlaner by a whole 4 levels. Assuming that it was because I was leaving lane too much, I go and look at my ADC's levels and he's not doing much better than I am.

So is it just me or does something seem off about exp gain?