I Recently Caught A Rash. On Tuesday It Was Only

I recently caught a rash. On Tuesday it was only on my neck. In Wednesday it spread to my arms, thighs, back and butt. I went to the emergency room on Friday and the Dr didn't know what it could be. I was told I can use calamine lotion for the itching. I applied the calamine lotion after a bath. After applying I noticed my skin starting to feel hot . Something like a fever , but only on the inside of my body. Is calamine lotion suppose to cause these feelings