yeah it sounds like mild SPD to me.
The pelvis is made up of 3 bones that are held together by ligaments in a kinda triangle. When the relaxin comes into the body to relax muscles it also relaxes ligaments and for some ladies it relaxes the ligaments that hold these bones together...the result is that when you make a movement like turning over in bed, getting off the sofa, and then if its really bad, walking, especially up the stairs, or any movement which involves you moving one leg independently from the other, then the bones move apart and together cos they arnt held tightly together anymore and thats what causes the pain.
I got it REALLY badly with James at the end of the pregnancy and unfortunately it seems to be returning now with a vengence.
If its really bad then see your midwife who will refer you to hospital for physio and also give you a belt thing to wear which artificially does the job that the ligaments should do (hold your pelvis together).
I would suggest seeing someone about it if you are in pain cos i ended up on crutches with james..
Also, wen you make a movement, try and do the same things on both sides. So when you stand up, do it with your feet together and if turning over in bed try not to move one leg over the other, use your upper body to rotate yourself instead. That should ease the movement of the pelvis and not cause so much pain.