A friend of mine had been stung a lot in his line of work (HVAC guy) and only in the past few years did it bother him to the point where he would swell up just like the OP described. His doctor explained that we do not build immunity with each successive sting but rather just the opposite...the sensitivity increases. So he carries the epi-pen everywhere now also. He also says to use a credit card to scrape the site of the sting (to remove the stinger) as soon as possible. Those things are nasty and can build a nest in a day or two. In my first house the builder apparently mis-measured on the number of trusses needed for the garage so built one on site. The gussets were full of wasps so I waited until evening and sprayed them all. By morning there were probably 1,000 dead wasps on the floor. I've gotten nailed just opening the lid on the side burner of a gas grill (in fact on my last grill I had to search for a model that didn't have a side burner). The valve cover on my LP tank is all beat up because they will whack it with a stick before they open it. In my last house I opened the door of a shed to get the mower and was immediately attacked by several. Fortunately it was a very hot humid day and my hair was plastered to my head so they just bounced off.