Here is something I 'discovered', so to speak.
All day last Wed I was suffering badly with SPD but also my bump and entire back was aching, not just my bottom and upper thighs.
I spent a long time leaning over my birthing ball, kneeling on the floor and making circles and rocking back to front, side to side whatever was comfy.
Later I got up and walked, walked not waddle like a pg woman off into the kitchen. No pain, anywhere at all.
Yesterday I went out with dd to meet my friend who I only see once a year as she lives in S'hampton. With 3 active kids between us in tow I knew it was going to a tiring day.
I ended up carrying my 3yo dd in my sling on my back for part of the time as well. When I got home, again, leant over my ball and did my thing. Today, I don't feel any 'punishment' for what I have done.
Moral of the story, I am spending as much time as possible over that thing.