First remove the pain. for this, i would suggest going to that clinician until the pain is gone.  i don’t think it’s a good idea to recommend stuff here if you feel pain.  that requires direct attention to what really is going on.  work with him/her until the pain is gone.

Next, I think the treatment would be a plan of improving posture, improving stability in the lumbar spine, more mobility in the t-spine. i’m not sure what a “dead” psoas really means, but most likely it sounds like it is very taut and the muscle is in a short very weak position and needs to be lengthened.  There are numerous methods for doing all that, including videos on MWOD.  why don’t you make sure pain is gone first before we get into the above?