extremely itchy and stingy rash on legs.

I have recently been doing a lot of exercise and last week a rash on legs appeared which are extremely itchy and stingy. It is driving me mental I am trying my hardest not to itch but it's unbearable. I did use a different self tan so I don't know if it is to do with that. I have tried piriten and lotions but nothing is working! It also stings when I go 4 a shower so I have to use cold water. Any advice? i hate going to the doctors for things like this i feel i am waisting there time x