Well I found this to be very interesting:
"No one knows why SPD occurs for sure, or why it happens in some women and not in others. Some ethnic groups report a high incidence, especially Scandinavian women and perhaps Black women. Other risk factors may include having lots of kids, having had large babies, pre-existing problems with this joint, past pelvic or back pain, or past trauma (car accident, obstetric trauma, etc.) that may have damaged the pelvic girdle area. It also seems logical that women who have broken or injured their pelvis in the past would probably be prone to this problem.
Some sources view SPD simply as a result of pregnancy hormones. As noted, the pregnancy hormones relaxin and progesterone tend to loosen the ligaments of the body in preparation for birth. One theory is that some women have high levels of hormones before pregnancy, and then additional pregnancy hormones cause excessive relaxation of ligaments, especially in the pelvis.
Another theory is that some women manufacture excessive levels of relaxin during pregnancy, causing pelvic laxity. However, although still popular, this theory seems to have been disproven by recent research. Another theory is that women whose joints are especially flexible before pregnancy may be more susceptible to the effect of hormones, or that some women's bodies are just more affected by hormones than others. Traditional medical sources tend to view the problem of pelvic/pubic pain (when they acknowledge it at all) as simply a hormone problem.
A different theory holds that the problem is structural instead, and usually results from a misalignment of the pelvis. In this view, if the pelvis gets out of alignment, the bones don't line up correctly in front, and this puts a lot of extra pressure on that pubic symphysis cartilage. If the two sides are not aligned, it restricts full range of motion, pulling on the connecting pubic symphysis, and making it quite painful. The more out of alignment it is, the more painful this area becomes. It also tends to affect the back, especially in the sacroiliac area, since the pelvis and back are interconnected and work as a unit. And since many areas are affected by back problems, pain can also extend to other areas too.
Kmom's personal opinion is that this condition is probably primarily a problem of misalignment, although hormone levels and sensitivity to hormones may also play a role. In her opinion, the first line of SPD treatment should probably address the possibility of misalignment. Others may not agree. But whatever the cause, SPD is certainly annoying and painful to deal with, and Kmom knows this from personal experience!"
I do think, in my case, its a misalignment issue as I have had other problems in the past with my sacroiliac, which was successfully treated by a chiro. I do by nature have slack joints so I can see having a predisposition to SPD as well, although I did not have it with my previous two pregnancies.
Sarah I'm sorry to hear it has gotten that bad for you and nothing has worked. I understand how discouraging that must be and you have a right to be crabby about it. Im crabby and mine doesnt sound nearly as bad. I am going to try chiro though and see if it is another alignment issue. Im not sure about yoga just yet. My yoga teacher is awesome and wont let me do most of the poses and was all over me during class but I was SO frustrated not being able to do the poses. I love my yoga class for many reasons, one being around so many wonderful pregnant women and we take time to talk before class as well. My teacher is very kind and nurturing and I may continue even just do work on my breathing and relaxation. She is very affordable and something I enjoy just for me.
That plus size pregnancy site has a lot of great info for everyone. I saw it in my google search and didnt click on it thinking it didnt apply! Maybe they should change the name. :-) Reading all of the restrictions for birth positions is kind of daunting though. It says over and over again hire a birth attendant who is familiar with SPD and its making me really consider a doula again. Just not sure its in the budget!