What do you mean by “I cant make changes using the “per page options”.
Do you mean these options are not there, or that when you use them they produce no results?
EDIT: If they are not here, see Weaver’s answer below as the likely issue.
If they are not there, then you may be missing the Weaver Xtreme Theme Support Plugin, or it may be deactivated.
All the per page options are in that plugin, so make sure it is there and activated, and eventually, delete it and reinstall the latest version from WordPress.org