I have had a small about size of pencil eraser scab on my butt for about 7yrs. it goes away and comes back. only crusty/painful if picked ?

Virus: It sounds like a viral infection, and could be a herpes infection. I recommend seeing your doctor when you have a new one so it can be cultured. It is very treatable but also contagious.

See MD: Do not pick or scratch the area. Have area seen by dermatologist or surgeon, as there may be a sinus tract that needs to be removed in order for it to heal. Keep in mind you can cause a serious infection if you pick at it.