I am suffering an acne problem on my buttock area, which I apply Fucidin for several days, I don't have diabetes, hygiene is good, what is the cause?

Could be many things. An outbreak of acne like rash on the buttocks can happen from a variety of causes. Excessive sweating even with good hygiene can promote bacterial infection and the types of bacteria that can cause this are treated differently. The fucidin cream you are applying doesn't help adequately and you may need an oral antibiotic.