Here's a piece of sql that will help you find the date of the first monday of a given year and month.
TO_DATE(CONCAT(CONCAT(?Year?,?Month?),TO_CHAR(TRUNC(DECODE(TO_NUMBER(TO_CHAR(TO_DATE(CONCAT(CONCAT(?Year?,?Month?),'01') ,'YYYYMMDD' ) ,'D')),1,2 ,2,1,3,7,4,6,5,5,6,4,3) ) )) ,'YYYYMMDD' )
In...