I have SIJoint problems and since my 2 level fusion i got a metal plate and clips in a pelvic area. Did it work? Nope, I have more pain in that area, hip, tigh and bottock than before surgery.
One thing I can tell you: being Ortho does not mean he is familiar with SIJ problems and can diagnose you right. Unfortunately no test showing any problems, only a good knowlegable in SIJ Dr can diagnose you. It actually takes 5 min for him to know exactly where the problem is coming from.
My Dr who operated on me - had no clue about SIJ even though I was telling him about my symptoms. Only during the surgery he saw what this was exactly.
Good luck to you and don't give up!