Swelling, Itchy Rash And Pain On Left Side Of Body, Any Suggestions Please

Hi had a real bad, painful and infected abssec that was drained a month ago on my left leg (back). In the midst of healing I developed allergic reaction to the sulfur in my bactrim (antibiotic) so i discontinued. then i developed a sever rash around the wound where the abssec was i believe due to the tape/band aides. But now I have pain and swelling on left side of my body. Painful and almost like a burning feeling. I am itchy all over but mostly on the left side. What is it. I have been to ER, general practitioner and OBG. taken blood, work, urine samples, sonograms but they are all negative. what can it be? Dr said he does not think its shingles . swelling, itchy rash and pain getting worse. please, please any suggestions would help.