Could have been a deerfly.
I had one bite the back of my hand 2 years back and it swelled up.
I took some benydril (antihistamine) and it was fine.
Damn fly is colorful and looks harmless.....until it bites!
OK I read this on line awhile ago ---but---never tried it.
Tape a penny over the bite. It's supposed to cause the swelling to go down.
I know,I know ,It sounds stupid,but what can it hurt