What Causes Burning Rash On Testes, Anus And Buttocks?

I have a rash on one of my testes and around my anus and buttock for the last few days. Very uncomfortable and burning sensation. Hurts when I lie on it or sit down. However, no pain when I pee and no deposits in pee e.g. protein (had urine test beginning of this week at doctors). I would be grateful if anyone can help? Many thanks