page reload

 I am running certain AddBG function in Page_Load event. I do not want AddBG to run if somebody clicks on reload button on the browser or if someone hits a back button on the browser. I used IsPostBack to do this but AddBG still runs on page reload or back button press. AddBG should only run if user comes on this page from BG1Page.

How do I do this?
my code:

protected void Page_Load(object sender, EventArgs e)
{
   if (!IsPostBack)
        {
            AddBG();
        }

}

...