Where are ascx Controls Called From???

Hello,
I have an ascx file where I have defined bunch of controls. This file gets called from three different aspx pages. 
I populate the text boxes with values from back-end DB when called from modify page and write to DB when called from insert page. 
I want to make sure some of these text boxes are disabled when called from modify, as the data is populated slightly differentlty in different conditions. And the user would need to modify the total number from a different page to change the numbers in these controls. 
I have an init function in ascx.cs that initializes these controls and sets enabled = false. But how do I conditionalize that init function, so that it is called only when  the ascx is loaeded from modify page and not called when ascx is called from insert page. 
Or is there some other way I can find that? I am doing get/set in ascx.cs file, but not sure if I can enable or disable these text boxes f ...