I am a big time crier when I cut up onions. Usually to the point where my eyes burn so bad, I have to walk away for a few minutes until I dry up. This can make cutting up onions a long and painful process for me! Here is what I have found to conquer this:
As you are cutting up the onion, breathe through your mouth instead of your nose.
As simple as it sounds, it has worked wonders for me! Try it and let me know if it works for you, too!