Hi Jitesh,
You can find the same via Standard or customized report. You just need to take out report for last three month and sort the same on customer and sales area.For SAP standard reports you can search the same on Forum, Check this link http://www.erpgreat.com/sap-sd/standard-sap-sd-reports.htm
Regarding the tables you need to specify that your requirement is based on Sales order or Billing ? For table linkage you can refer to this document
http://www.recercat.cat/bitstream/handle/2072/5419/PFCLopezRuizAnnex3.pdf?sequence=4
Regards,
Rahul