What Causes Deep Sores On The Buttocks?

I have sores on my right butt cheek that have been there a long time had a biopsy done they said it is from a bug bite, but no one else in my family or household has any of these. They make deep sores and round about the size of a pencil eraser. I have a inside dog but he is bathed 3 times a week and every thing in my house that can be washed in hot water and bleach is done. I change my bed lines 2 or 3 times a week and my house is very clean to the point I am constantly cleaning. Please help if you can. My e-mail is YYYY@YYYY .