Dude I think you may have given the correct name to what I experienced about 3 weeks ago.....the pic of your foot looks exactly like what I had.

Starting at my right ankle I had an itch that felt similar to a bug bite, except there was no sign of a bite. Next day it looked more like a spider bite than a bug bite but still no sign of the bite. Third day I was like you were on Saturday and I went to the doctor the next morning when it was no better.

Same treatment as you plus they treated me to bloodwork to rule out Lyme's. After 2 or so days of Antibiotic it started to improve...mind you during those two days it was just as bad as it was on day 3 and 4, but it takes some time for those pills to build up to a level in your system that they actually start to work (that's where you've got the IV advantage!).....doc told me to take the antibiotics for 7 days which I did....I was pretty much back to normal by day 7 with just a little residual itchiness.

My doc never actually told me what it was....they just treated it some sort of infection (insect caused or otherwise) and gave me antibiotic. Lyme's test came back negative.

It definitely took 2 weeks start to finish to be back at 100%. I was off the bike for nearly a full two weeks because it was excruciating to bend my ankle when it was really inflamed.

Ibuprofen helped keep the swelling down for me.
Not fun though....Not something I'd like to repeat anytime soon and now everytime I've got an itch on my ankle In the back of my head I'm like "Oh man, not this again"

As Little Darwin suggested, I too was worried at first that I had Gout.