The above book helped me tremendously. At 39 weeks I have pretty much just some discomfort in my pelvic joint, but nothing like before. I chalk it up to having a good chiro and that book. As far as birth goes, avoid laying on the back at all costs to deliver. When I had this with my daughter, I gave birth on my hands and knees no problem despite the SPD.
IMO, ditch the OB.