How Can Penis Shaft Dryness With Peeling And Irritation Be Treated?

i have red leathery skin along the back side of my penis shaft. My doctor said it was jock itch and gave me a prescription cream to put on it. It's been a month now and it has not gone away. The skin gets very dry and peels off and it very irritating to touch. Is this an STD? I have not had unprotected sex either.