I had spd with my last three pregnancies and I feel for you! I found that doing the exercises that I was told to do (after my pelvis dislocated in my second pregnancy - first with spd) really helped with the physical severity of the problem. I felt more stable but the pain was still there. I continued doing my exercises daily - mainly out of habit - and then found out I was pregnant again I was glad to be feeling stronger in my pelvis. It got painful up at the end of pregnancy but much more manageable. In my last pregnancy it just gave me twinges on and off and wasn't too bad - until I tried to roll in bed!
Two years on, I am thinking of seeing a chiropractor because I am still not 100% but not too bad either.
My favourite position that worked for me was birthing on all fours leaning over a chair or firm pile of pillows. I liked this position because I could choose how far I wanted my legs apart. The midwife attending my birth commented that I could do with my legs a little wider apart and I explained to her that at the end when the head comes right down I will adjust my position - and did, naturally and when I wanted to.
Be confident in your body and see about some strengthening exercises - the really do work but take a while for you to notice the effect. ---- good luck