Reporting Services :: Displaying Previous Months On The Basis Of Start Date

I have a ssrs report which has a parameter start date.i have made 12 columns acc to client req which i cannot change:

jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec

These columns are dynamic acc to start date for which i have used this exp for first cell:

=monthname(month(Parameters!Startdate.Value),true) and for next 11 cells accordingly.

These 12 columns are grouped quaterly which i have made statically again for clien req which i cannot change so they are grouped staticaly by me in report like:

q12015      |q2  2015     |q32015      |q42015
jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec  

exp for quarterly is :

="Q" & DatePart(DateInterval.Quarter, Parameters!Startdate.Value) &  year(Parameters!Startdate.Value).

Now when i select my start date of months jan,apr,july and oct report work fine.... but when i select my start date months of feb,may,aug and nov then reportis something like: (lets say i choose feb)

q12015        |q22015     |q32015      |q42015
feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec|jan.

What is happening is in q1 feb,mar and apr are coming and what i want in q1 is jan,feb and mar.

And in q4 nov ,dec and jan is coming and what is want in  q4 is oct,nov and dec.

So generally what is am asking is how to display jan in this condition in my first cell.same apllies for rest of months..

Similarly when i select my start date months of mar,june,sep,dec i want previous two months to be displayed.