Ouchh! Painful Lower Spine

Some of you may have read my post about my pony's bouncy canter. I'm not sure if this has anything to do with it but ...
The lower part of my spine and coccyx is unbelievably painful.
I don't know when I can ride again and if it will just make it worse.
It started hurting a few days ago and it's just got worse. I'm up and doing everything as normal (except riding) but even the tiniest movements send spasms up my spine. It's so annoying and it must be riding. Has anyone got any ideas as to what caused it? Or has anyone had similar problems?
Thanks x