What is the need to use parameters for this scenario.this can be achieved using a filter on actual date . if we set the date field to "continuous", you can use a relative date filter of the last 3 months (u can customize it if you want ). This will always just show the last 3 months. If desired you can also show the discrete date filter with "relevant values" turned on, so they can drill into just a particular month.
Thanks for the replay.
Here i am using 10 data sources i have to filter the data in all graphs.