What kind of testing have you had done to determine if this is herpes?
You can have herpes on your butt - I get outbreaks there, and I swear the *** herpes, as I call it, can be worse than any outbreak on your genitals. Genital herpes infects the sacral ganglia nerve group, so you can get outbreaks anywhere in the boxer short region.
Are you getting frequent outbreaks? You might think about suppression - taking valtrex (convenient once a day but expensive) or acyclovir (twice a day but way cheaper) daily to reduce outbreaks.
Aj