My husband for the last few months has been breaking out with small itchy painful sores on his back inner legs an butt , what could it be?

Furunculosis: What you are describing sounds like furunculosis, a bacterial infection of the hair follicle that progresses to a boil. Often, it is caused by staphylococcus bacteria and should be evaluated by your doctor so the puss can be cultured and antibiotics prescribed. Sometimes the staph can be the MRSA type, which is a severe strain that is resistant to many antibiotics. Have it checked out.