Caching tables not clearing out
Sounds like you probably have a stuck or error'd "Delete Stale Template Cache" task.

You can tell if a task is stuck because there will be a circular progress bar in the upper-right hand corner of the CP that isn't progressing.

If it error'd, it will be red and you'll have the option to re-try it.

Regardless, here's the general troubleshooting steps necessary for both cases: http://buildwithcraft.com/help/stuck-tasks