Any ideas what this reaction to an old bug bite could be?

A few weeks ago I got bit by some type of nocturnal insect. It looked like a cross between a moth and a horsefly. It took a chunk out of my leg, and it swelled up and turned red. The next day I had a bad reaction to the bite, the whole shock thing and had to get a steroid shot. Now the site of the bite has swelled up again and it feels like there’s a small ball or something in there. Any ideas what this could be? It’s been two weeks so I’m not worried about the bite, just curious.