yes, it is possible.

The site of the original infection was not your buttocks but rather the genital area, vagina or anus, with some sort of sexual contact.  People don't get an initial infection on the buttocks because the skin is too thick for virus to penetrate, but once the virus is in your body, it can and often does travel to the buttocks for recurrences.  So either you missed the initial genital infection because the symptoms were mild or you confused them with something else OR the initial infection was asymptomatic and you are noticing only recurrences.  When someone has lesions only on the buttocks, they will also intermittently shed virus from the genitals as well.  Buttocks herpes IS genital herpes, though I know that may be hard for you to hear right now.  The virus can travel to any branch of the sacral ganglia to get to the surface of the skin - yours seems to prefer that right buttocks, but that's not the only place it can or does go.

Terri