Shelley,
I remember when Dr Togut would talk to us he would say whatever you do to start small, take breaks, and take time to work up.
Around the track three times with sacro problems and the tos is overdoing it for you, your not a 16 year old.
Your nerves are inflamed, sounds like two things the sacro-illiac and the TOS. Nerves insert into muscles to tell them how to move the body. When you assult inflamed nerves the muscels try to protect them and can cause spasms.
Another thought, you may have been dehydrated, or lack potassium in your body.
I cannot walk, I try the treadmill, but it is sore, my best walking is laps in the theraputic pool. I can use a floaty for my arms and there is no stress or pressure on my back and hips.
Your sacro-illiac problem likely has that leg a bit shorter, so your stride is off too...
Maybe if you did one lap, and sat, then a secondlap...stop for the day.
Or even a half lap, stop and the rest of the lap...for a week....BUILD IT UP SLOW, your body is not a healthy16year old. your injuries liken you to an elderly person, would you have your grandma walk three laps?
So unfortunatly, remember you are injured, rehabilatating yourself and treat yourself that way.
If you can, get gatoraid, and regular old asprin to help with the spasms.
Hopeing you feeling better.

Di
PS Katie says your are the Best, you are her hero and love. She is recouping from bronchitis and well entertained. She will drop a note to you.