What kind of bite/sting is this?

I was working on a project outside in a sports bra and felt this surge of pain right under my armpit. Swatted and saw some sort of insect (bee or fly) flew away slowly. Somewhat small, but black/dark color.

Area felt so tender and weird. I was in a lot of pain and discomfort. Still tender. Any idea what kind of bite/sting this is? I had a hive like reaction and the right is current state.