What Causes Brown Itchy Patch On Buttocks?

I have this brown itchy patch on right buttcheek. Started out oval shape then got slightly bigger. There is also tiny red patch above the brown patch. I also have another small round brown spot on the crease of buttcheek and leg. Only thing that works is cortisone 10 eczema lotion. I've been using it for 7 days already. It gets worse in evening. I put coconut oil in morning and throughout the day but still gets worse in evening. The cortisone lotion is 1%.