Forms Data Controls :: Paging Gridview: Pages Not Showing Up?

I have a web app where everytime I upload an Excel file, its contents appears in Gridview, which is binded with a DataTable. Using the properties, I have set paging and sorting to true.

When I input a file using fileupload and a submit button, the web app has page numbers at the bottom appear.

It also correctly sorts it, (my page size is set to 10), however, when i click on the next page (pg 2, for instance), nothing shows up until i upload the file and hit submit again.

This is the code in which I build the table:

protected void AddResultToGrid(String url, String result)
{
data = (DataTable)Session["URLSessionData"];
DataRow dr = data.NewRow();
dr[0] = url;
dr[1] = result;
data.Rows.Add(dr);
gdvResults.DataSource = data;
gdvResults.DataBind();
Session["URLSessionData"] = data;
}