Oversized Mosquito Bite?

I got a bug bite two nights ago. It was normal size for about an hour and a half, then it grew to the size of a quarter. When I woke up the next day, it was the size of a silver dollar! Now it's almost as big as my palm, and hot and a little tender to the touch, but doesn't itch as much as it is sore. Does anyone have an idea as to why this may be?