^What Cross-stitch said. My right side - the side that's attached to my right arm and my right leg. But if there's any question when you're describing your pain to your doctor, you could always point to the area where your pain is, too. My LRQ pain is always in the same spot, I could draw you a map. Maybe I should just get a tattoo over where my pain spot is! "X marks the spot!"
(and if it is a butt pain, it is a pain in the ass!)