Does your toilet ROCK?
If tightening the bolts on the base doesn't stop it, buy some plastic shims from a hardware store and slide them under the toilet to stabilize it.
If there's caulking around the base, you may have to remove it to slip the shims under the toilet.
Re-caulk after installing the shim to finish.
If you need help with this or anything else, feel free to call me.