Thanks kazbern,
My physiotherapist actually prescribed an SI belt, but she said it was more for sitting. Personally I found it quite uncomfortable and stopped wearing it (and when I mentioned to my rhematolgoist at a later appointment, he said not to bother with it).
Now that you say it, it does make sense why the stationary bike doesn't work. Unfortunately, the one that we have is a regular upright one, and I'm not gong to go out and spend the $ on a recumbant, when chances are, it will cause pain too. Really wish I could do the eliptical.
Didn't realize that yoga is vigorous. i always thought of it as stretches and poses for strength...kind of like some of my physio exercises. Good that you've found somethign that works. If i remember correctly, you used to be an avid jogger (I apologize if I'm mixing you up wtih someone else)