I'm assuming when you were treated for the "shingles" that your doctor asked if you had chicken pox in the past and you said "yes" and I'm also assuming that when he examined you you had symptoms that would clarify that diagnosis of shingles - painful lesions that run along nerve pathways.
That being said - i don't know at what age the rash on your buttock showed up - was it after sexual experiences had happened in your life - opening the door to a possible exposure to HSV1 and 2?? Do they typically show up in stressful times?? Is the test being run for the herpes IgG or IgM??
I hope thes equestions offer some clarificatin or encourage you to talk to your doctor and get more information.