What Do Painful Rashes On The Calves Indicate?

I have a very painful rash (that always starts on my calves) that is blistering and oozing as well as swollen. I have had this rash 2 times before both being in summer ,this time being nothing compared to the serverity of the first. It spreads like wild fire and begins scaring dark purple before the rash has even healed. I have been to my Primary Doc and I feel he is just not helping figure out the cause. He has diganoised with poison oak/ivy as well as folculitis but with both diagnoses neither steroid topical and oral treatments worked.I have tried everything vinegar,oatmeal,cold and warm compresses, sumac drying cream,calomine lotion, I can t be seen until Monday and its getting so much worse I am hoping you can shed some light onto what other infections it may be? or maybe some other treatments that will be more affective?