rash on legs

Hi.  I have been prone to getting a rash on my legs starting at my ankles and foot and working it's way up my leg whenever I am outside barefoot.  This will occur no matter where I am outside- in my backyard, at the beach, at a park, etc.  The rash starts out as a small red dot and it gets bigger over the course of the next couple of days.  They will sometimes end up as large as the diameter of a kiwi and when they are large they are more swollen and slightly painful.  If there are a lot of them it is more painful.  they are bright red and generally are circular until several days out where they can become more oblong shaped.  Another odd part is that they will primarily show up on my left leg and they always go higher on my left leg.  That is not to say they don't show up on my right leg, however.  I have tried benadryl thinking it may be an allergic reaction, gold bond powder and lotion, hydrocortisone cream  all without much success in reducing the rash.  No one else who is outside and barefoot gets them so it is not fleas or chiggers.  I am curious to see what you have to say about this situation.  Thank you, Doreen