Hi Laura, Sorry to hear you're feeling so crummy.
I think any rheumatologist who read your post would gasp - most know that exercise is key in the prevention of fusing, providing you are physically able, of course. Obviously if you're in an acute/active inflammatory phase, and in terrible pain, you're not going to be able to exercise (and for me, I know that will just make it worse). But when things are sort of kinda in control, and pain meds are working, light exercise/stretching is usually encouraged.
I think the bottom line is - if you find something that works for you, that helps your pain, increases flexibility/motion, and gets you moving, any doc would be silly not to encourage that. This illness is so individual - just do a little experimenting and do whatever works best for you. Hang in there.