I'm a male in my late 30's in California. I'm experiencing something very similar. I had the same looking rash on both legs about a month and a half ago for the first time. Thought it was some sort of bites since at around the same time I started a vegetable garden and spent a lot of time in my yard. Itchy red rashes on the bottom of my legs, swelling around the rash and ankles. I used tea tree oil to sooth the itching. About 5-6 days later most of the rash was gone. Yesterday I got the same exact rash again in the same spots. This time it was worse. Swelling on my right leg is much more noticeable than the left. By night time I had dime sized blister filled with water on one leg and a much smaller blister on the other leg. Overnight the swelling subsided, but now I'm starting to notice the swelling is coming back. I have a feeling this is something a bit more serious than a random rash, at least in my case since I've now had it happen twice.
Well I haven't heard from anyone. But after about 5-6 days the "rash" has gone way down. I must have been either allergic to something or got an abrasion from putting my skin on a bench to do a one arm row. Either way, I used topical steroid and Iced it several three times a day. Now I am down to twice a day and it is much better. Hopefully, this helps someone that has this. I have eczema and am allergic to many topicals and a few antibiotics. So I have seen this happen before. I knew it wasn't a infection as I had no pain (it was itch) , no fever, had no cuts on it and no bite from a spider or insect.