Suggest Treatment For Swelling, Pain And Rashes Due To Insect Bite

i was bitten by what I thought to be a horsefly early yesterday morning. Last night it was a little swollen, hard , and red. This morning it was much larger, very sore, swollen, hot to the touch, and red. I went to urgent care where I was told to continue the benedryl and cold compresses I had started at home. During the day it has gotten larger still (about 7 inches across), is very hard, hot, and tender to the touch, and has a few very small water blisters in the center. No fever- feel sluggish and yucky; most likely from the benedryl. When should go back to the doctor.