I have an allergy to onions where the fumes from them make my throat close up is this common and what do I do?

Avoid them. Sorry. Just stay away from the kitchen when they are being cooked.
Avoidance. This is not an allergic reaction; it is an intolerance. There is nothing you can do to treat this. What i usually do when chopping onions is do it outside on the patio, when there is a breeze that prevents me from having to inhale the fumes.