Aha, this happens very often. When you are cutting into an onion, you are breaking its open microscopic cells, which is full of enzymes that transform volatile gasses when they escape. Which naturally leads to a chemical reaction creates a lachrymatory agent. And there are some ways here for you to stop it. I tried them. They worked well. You can choose to use a sharp knife, which will help cause less damage to cell walls. When you are cutting into an onion, try to make the exposed side away from you. Besides, before you cutting, you can put the onion in the fridge to be frozen for a while, which will cause less propanethial S-oxide will evaporate. These are very useful and simple ways. I am sure they can solve your problem.
Your problem is very simple and common because it would be definitely easy for a guy to have such feeling when cutting onions or peppers or chillis. For those foods are highly irritative out of their nature, but the burning effect would go away within some time so you don't have to worry about it. But please do not rub your eyes no matter how terrible you might feel because that will lead to infections.
It is said that onions contain stimulate chemicals, when you cut an onion, you break cells, releasing their contents. Aside from wearing safety goggles or running a fan, you can keep from crying by refrigerating your onion before cutting it or by cutting the onion under water. Use a sharp knife to cut the onion can also be help cause it can reduce the amount of the damaged onion cells.
Well, first, I have to say that it is very common for many people to feel burning and watering eyes when cut onions. So you do not need to worry about it. And according to some experts, there are kinds of objects in onions which have the irritant function. So when you cut them, it will irritate your tear system and make you just like cry. And also, it will just make your eyes feel burning. To get rid of it, there are many ways you can just have a try. For example, you can breathe through mouth while cutting onions and the mouth is open. And that can be effective. Also, to treat your burning eyes, after you have cut onions, you can just use some ice under your eyes, and it will work for it.