I still think lot of confusion is there.
So i will ask one simple question.What text you need to display in the header of particular column and how it needs to be derived.
Is it that you need to display the current month - 1 i.e Feb 2015 or whats the logic of deriving the same.
Forget about the variable you have in place.If you answer this then it would be easy for all of us to guide you.
Regards,
AL