I have a raised, very red rash all over my body. It started on my chest , and on the area here, you can no longer see the individual spots. My GP initially thought it might be pityriasis rosea , but changed her mind when I went back; she seems baffled as to what it could be. I therefore went to a walk in clinic which prescribed antibiotics , but I have seen no results. What do you think this could be and how long do antibiotics take to work?