Code the report so the control source of text box will change based on date or current month

[GinaFlan]

I need for the control source for each column to change based on the current date so the proper month's data will be displayed. I realize I can do this with DateAdd("M",-4,Date()) in my query, the problem is hiding duplicates conditional formatting and all of that. So instead of training employees to go into design view and change the control source in the drop down, it would seem like I could simply write code to make that happen. Like if the current month is October then Text box 1 = 7/1/2014 and so on. This is a rolling 3 month report. Is there a way?

[GinaFlan]

Also where would I put the code under what event?