Hi Ankit,
You can write the ABAP Routine in Data Selection Tab in your infopackage for the field CALWEEK or CALMONTH.
I suggest you can make use of TVARVC variable as well. Reading the from and to date details from particular TVARVC variable for data selection.
Your ABAP colleague should be able to help you.
Please check.
Thank you
Satish Waghmare