What should i do if i have hives right below my butt!?

Treat: Over-the-counter non-sedating antihistamines like Allegra, Claritin, or Zyrtec are helpful for persistent hives while sedating antihistamine like Benadryl (diphenhydramine) can be helpful for acute hives. If you have persistent lesions targeted specifically to the buttock region consider a possible contact reaction from underwear or other garments worn regularly. See an Allergist for further treatment and eval.