I Have A Rash At The Top Of My Butt

I have a rash at the top of my butt crack. Now it has spread to the skin around my rectum. It itches tremendously. I know it's not a cleanliness thing. It seems so deep that my skin has cracked open at the top of my crack. I have tried antibiotic lotions, fungus (tenactin and clotrimazole cream), hydrogen peroxide, powders and lotions. None have been able to cure my ails. Help!