How To Get Rid Of Dry And Dark Skin On Buttocks And Waist?

Hello Doctor, My skin is very dark near my butt and inner thighs compared to my rest of the body. my butt becomes dry most of the time. i could also see lot of dead skins on my butt and black marks on my waist. i think this dark mark on my waist is because of wearing tight pants. i apply moisturizer on my butt and waist when it becomes dry. How can i get rid of this dark skin on my butt and my waist? I am male/26 years old. I am going to get married in a years time and therefore you understand my problem. Since i have a year in hand can you suggest any remedy which can atleast make it less darker over time. I am a software engineer working in a regular shifts 10am to 8pm