Hi im high allergic to insect bites and was advised if a beestings me id go into anaphylactic shock immediately. ive been stung by something & the welt has swollen to the size of my hand. any thoughts on what it could be ?

Not really: The only way to know for sure what bit you was to have you see & identify it at the time. The reaction you describe is an arthus reaction, a common body protective response where the capillaries begin to leak to create a protective barrier of fluid to reduce the entry of toxins into the body. The reaction is not specific to a particular bug.