It could also be that your immune system is getting more sensitized to bee stings over time and exposure. Your next sting could induce systemic anaphylactic shock which could kill you if you don't have quick access to an epi-pen. Time to visit your primary doc or allergist.
That's what a doc told me after I'd gotten stung 2-3X one summer, and suddenly went into anaphylactic shock. My face turned white as a sheet and my crotch and the soles of my feet started itching so f$cking bad that I had to take off my sneakers and scrub them into the leaf litter to relieve the itching. (I was cutting firewood at the time, and got into some ground hornets.)
I probably got stung a hundred times when I was a kid, with no reaction, but for some reason those ground hornets that one summer did the trick. That said, a swollen hand and arm doesn't necessarily sound like anaphylaxis to me (not a doctor) but it couldn't hurt to have an Epipen handy, along with some Benadryl. (When I get stung now, I chew up 2 Benadryl while holding the Epipen in my hand, and if I think anaphylaxis is coming on, I figure I'll use the epinephrine.) Unfortunately, if you get a really bad anaphylactic reaction, you may not even have time to use the epinephrine. A friend of the family got stung while mowing his lawn, and he dashed to the house to get his beesting kit and dropped dead on his doorstep.
It's pretty sick how anaphylactic shock works: Your body senses the toxin or allergen (beesting venom, peanuts, shellfish, whatever) so it says,
"I'm gonna keep that toxin out of the bodily tissues by lowering the blood pressure to almost zero!" ... which ends up stopping your heart because there's not enough blood pressure to feed the heart muscle oxygen. You wonder how a software bug like that could possibly survive millions of years of natural selection ...