Show Previous 3 months data in cross tab webi

Hi,

I am having webi report which has Filter on year to month if current month is Nov 2014 then Report filter is Cal year/Period Jan 2014 to Oct 2014 based on that we have one tab. I have to create another tab where we can show last 3 months data also have to show month inside the tab.

In first tab we have

Month

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Second tab should be filtered on Aug, Sep and Oct. it is to be done dynamically so that in next month filter works on Sep, Oct, Nov.

Month  KF1

Aug     200

Sep     210

Oct     301

I want to know how we can give dynamic filter of last 3 months on particular tab and can show month as column inside the tab.

Thanks,

Ankit