Bee stings - when you don't know bio history of allergies

What have you done when you do not have a complete family history of allergic reactions from your children's biological families? With one of my son's we have a pretty thorough health history, but with the other it is terribly sketchy. I was on my way home from work yesterday when my sitter called to let me know that while swimming in their little pool and playing in the backyard a bee got in his shorts and stung him on the penis! I was about 10 minutes out and told her to give him some benadryl. When I got home he was still screaming uncontrollably and when I looked at his sting it was horribly swollen. Maybe because of where it was I freaked out more than I might have, but I scooped him up (naked) and drove him to the ER. They were very understanding and sympathetic to his situation, and said I did the right thing in giving him the benadryl. The instructed me to also give him ibuprofin and maybe claritin during the day for the next 3 days and monitor it. But later I wondered if I was over reacting. My gut told me that without adequate family history and given the location I was better to act immediately. But when I called DH to tell him I was going he kind of questioned why I was going to the ER for a bee sting. What would you have done?