Dovey,
 
This is a problem I had and thanks to KStar and others, have not had any real problems with since.  My SI issues started 4+yrs ago and I also saw different professionals with zero results.  Eventually with all of KStar’s videos, my PT friends, and my background, I put together a plan that worked for me and have had nearly 0 issues the past 2-3yrs.  I will lay it out for you in hopes that it will help.

In May of this year (2013) I asked Kelly at his seminar how often he sees SI problems and he said all the time.  He also said it is almost always over extension/tight anterior hip.  Every time I have checked anterior hip flexibility in someone with SI pain they are missing most of their ROM.  The QL is also a known cause of SI pain due to up slipping the ilium.  I would look at these 2 areas as your main cause of trouble, the QL (quadratus lumborum) and anterior hip.  So here goes.

1.  If the joint is out of place it needs to be put back in place first.  You are already doing this with your yoga block and squeezing it between your knees.  I know KStar has a video on this but I can’t find it.  This video shows the exact same movements that we were shown during his seminar for the reset.  If I can’t get it back into place myself I will go to my chiropractor and then attack the tightness when I get home.

http://www.youtube.com/watch?v=fGbkpGiLS1c

2. Attack the anterior hip!  I did the couch stretch and banded couch stretch up to 5 times a day, 2 minutes per side until I was finally out of anterior pelvic tilt.  If you are getting adjusted by a chiropractor and having it go back out as soon as you sit, it tells me your anterior hip is short. 

http://www.mobilitywod.com/2010/09/episode-29-use-your-tv-to-time-your-pain-hips-and-lower-leg/

and

http://www.mobilitywod.com/2011/04/episode-235-recover-your-anterior-with-the-super-couch/

3.  Attack your QL!  Again this is the exact same movement we were shown at the seminar.  If your QL is too tight it will eventually pull your hip upward (this is an up-slipped ilium).  I eventually realized that a spasming QL was the driver of my SI problems almost every time.  Throw an extremely tight anterior hip into it and I ended up with an up-slipped ilium with anterior tilt.  My up-slip was severe enough that it was super easy to see in the mirror.  If you feel out of place but aren’t sure, look up how to palpate the Anterior Superior Iliac Spine and place a dot on each spot.  You should be able to see the difference in height from side to side if you are out of place.

http://www.mobilitywod.com/2013/02/the-ql-is-not-a-boneeven-in-the-matt-chan/

To sum it all up: 1. If it’s out of place put it back in place.  2. Tight anterior hip causes SI pain  3. Tight QL drives the up slip.  Be diligent with your treatment.  The old KStar prescription was 5x/day, 2min/side.  Also, look at your sleeping posture.  If I sleep on my left side, it cause my right QL to spasm.

I know this is daunting, but there is hope.  This was the majority of my lower body mobility and still is.  I hope this helps.