Skin Lightening Treatment for Lower Butt Area?

What Skin lightening treatment do you recommend to even out and lighten my skin on the lower butt area? My backside are gets darker as it goes higher. I am satisfied with the skin tone of my legs and thighs except for my lower butt. It's very dark. I've been using Proactive skin lightening lotion for the past 2-3 days to see if it'll lighten up. I don't know what else to use.