You are having Tinea corporis over the buttocks. This a fungal infection which is absolutely treatable with appropriate antifungal treatment.

It's Fungus  infection....common around skin folds like thighs and genitals.. avoid sweating, sharing clothes,towels and soap.. specific medicine required depends on the severity.. for detailed prescription do direct online consultation

The pictures provided are quite clear. And the history of itching also helps in diagnosis. Yes this is ringworm, which in scientific language is tinea cruris. It is completely treatable. I need to know few questions before prescribing you medicines: Since when do you have this? Do you have any other disease for which you are taking any treatment? Are you applying anything on this? Have you taken any treatment for this? Any family member has same problem? Please respond to these questions, I will be able to guide you better.

Any other medical illness Any treatment so far