If your pitchers are doing well then there is no reason to bench them. You dont have to worry really if your roster is full of quality pitchers. It's far better to hit your innings maximum a little early, then not hit it at all. If your pitchers are struggling then you can certainly afford to bench them if they have an unfavorable matchup, but this is nothing to panic over. Your pitchers are probably just going a little deeper into games (not a bad thing, usually means they are pitching well), and your relievers are probably being use a little more often (for example, Javy Guerra has been used in 9 games already while Joel Hanrahan and Jordan Walden have been used in 4 games a piece. This usually evens out as the season goes along). Again, this isnt anything to worry about. 6 starters should usually average between 180-200 innings if they stay healthy, while relievers can go anywhere from 50-70 innings a piece if they stay healthy. You are looking at about exactly 1400 innings going by that logic.
If it gets to be July and you are projected to go over you innings limit, try and trade away your lesser pitchers unless they are at petco park or something like that. You are gonna want to make sure you get you every start from your best pitchers, so if you run out of innings in the beginning of september, then you might miss out on 4 or 5 starts from guys like Jered Weaver or Clayton Kershaw because you maxed out a bit early.
Again, you should be just fine, I wouldnt panic for now, it isnt a bad thing if you max your innings a little early, its better you reach it then fall a few innings short. You dont get any credit for having leftover innings at the end of the season, so make sure you use them.
This is a problem you should re-evalute around the all-star break, it isnt anything to worry about in April.