What Causes Itching Red Rash All Over The Body?

I woke up this morning with an itchy red rash all over my body. I spoke to nurse at the Royal Marsden who suggested I went to my local walk in clinic. I was prescribed pitiron from a chemist over the counter. I have taken two tablets - one at 12 midday and one at 4pm. The itching is still pesent and also the rash. I am not sure what to do next. the chemotherapy drugs I am on are paclitaxel and carboplatin