C# - Cache Page But Count Hits?

I have an aspx page which counts every visit and creates a cookie. But if I use OutputCache page counts only the first visitor who requested the page. How can I prevent this bug?

Page directive:

<%@ OutputCache Duration="1200" VaryByParam="mode;page;sid;tid" %>

Codebehind:

protected void Page_Load(object sender, EventArgs e)
{
//Load single post data
#region Hit Counter
//hit counter lasts during session
if (Session["LastHit" + postId] == null)
{
cmmnd.CommandText = "UPDATE Posts SET Hits=Hits+1 WHERE PostID=@PostID;";
cmmnd.ExecuteNonQuery();
Session["LastHit" + postId] = 1;
}
#endregion
}