I third the swimming!

Rather than rewrite good information, I recommend this link on Pubic Pain (don't worry about the 'plus-size' bit...it is general info, relevant to all SPD)
Pubic Pain
The article covers everything from what it is, what you can do during pregnancy and in regards to birth, this article goes into detail with the following:

"Planning for Birth

Certain common obstetric interventions tend to make Symphysis Pubic Dysfunction pain worse, and may even lead to ligament damage or severe separation of the joint, causing true Diastasis Symphysis Pubis. Therefore, it is vitally important that your doctor or midwife understand and believe in the existence of SPD and realize its implications for birth. The following ideas (taken from a number of sources) are supposed to help maximize your comfort and help the normal birth process, while also minimizing the risk for pubic symphysis-related trauma.

1.Be extremely careful of birth positioning. Certain positions are better than others. Avoid stirrups!
2.Be sure your labor assistants and providers know all about SPD, what movements can hurt or damage you, and what your comfortable range of motion is
3.Avoid most common labor interventions, as these often cause pubic symphysis strain/damage
4.Avoid an epidural if at all possible, as this often is associated with more severe damage
5.Use a 'narrow gap' between the legs for any routine procedures that can't be avoided
6.Hire a birth attendant that is familiar with and can help resolve baby malpositions "

All the best. xoxox