No answers for you but plenty of empathy. I have had some issues over the last 4 years off and on with low back, hip, IT band etc. It comes and goes (pulling out of a minor flare-up right now) but nothing as painful as what you describe. Keeping my fingers crossed that you can find the right person / right method to get this fixed. For me it was a combination of massage, PT, rest... and some mysterious component of time or chance....
2016 Specialized Ruby Comp disc - Ruby Expert ti 155
2010 Surly Long Haul Trucker - Jett 143