I have a problem of rashes on my buttocks with dark patches.... please suggest me with some cream docs to remove all such patches?

See a dermatologist: I think you need to know what is causing the rash. Do they first look like pimples? You may need a biopsy.

Itchy or not?: If they don't burn or itch, one would think about an infection. If they itch, one would consider an allergic contact reaction . If you were much older, one would think about skin cancer or bruises. So until you can be more specific, it is impossible to even make a guess.