I have to agree with yowsy123's comments. It seems to be like neural in origin as some of the movements you mention tension the nervous system. I good clinician should be able to use that to diagnose your problem segment. It could be that some musculature may be involved in the gluteal region such as piriformis but the symptoms do not sound like a muscular issue. I'd go for a one off assessment and home mobilisation plan and see how you get on with that as a starting point.