Red very itchy rash dr aid she didn't know what it is all over back chest inner thigh neck arms shoulders had for two days bad itchy skin

Many possibilities. There are many things that could cause the skin to itch. Several types of inflammatory conditions of the skin, allergic reactions, and sometimes bacterial, viral or fungal infections can cause rashes on the skin. Insect bites can also be the cause of a rash on the skin. Have it evaluated by a professional and get the appropriate treatment.