Hi Vishal,
Create variable to get month year number in format MMYYYY
and use this variable along with the month name field and hide it.
For multiple years the month name will repeat but not the month year number. so you will not get multi value error
=[Year]*100+ToNumber(FormatNumber([Monthnumber];"##"))
this will give values like 201505 and 201405
and corresponding to this you will have May(MTD) and May
One more point is if you are showing data for multiple years then you should be showing Month and Year in the crosstab rather than month alone. April 2014 May 2014 ..April 2015 May(MTD) etc