There are quite a few here on BB that have or have had SPD.
Can you afford a physio?
I have a great physio that I can go and see only when it gets too much. I think some will get you in a little too often IYKWIM. Even if you just have a couple of visits to get an idea of how it is treated and the excercises to help improve you SPD it can be a great benefit for you.
My SPD has bad and not so bad days. As much as it kills me I still get down on the floor or use my fitball and do my excercises. I'm sure that by keeping my muscles toned as best I can it will help keep it all together down there. I haven't needed to use a support belt and think that with only a couple of weeks left of my PG that I won't need to. When it's really bad I don't leave the house unless I have to.
It makes life difficult but you have to look after yourself.
My boys know that I won't pick them up. I refuse to vaccuum and have told DH that if he doesn't help I will get a cleaner. The kinder teachers don't ask me anymore to help out with kinder duty as I can't do much.