Graphics question

I have created a webpage that builds a table and graph using the GD functions. When I switch to another page or select a different month to build the table for, the graph.jpg does not rebuild. I have to press reload to make the graph render using the new data. I have used imagedistroy($pic) in the hopes that this will work, but it didn't. To elaborate on the situation, I first call imagecreate, then run the code to create the bar graph. I then use imagejpg($pic,$graphname) (or something ot that affect. I don't have access to the code at home). I then show the picture using echo "<img src=\"$graph\">"; Finally I call imagedestroy($pic). Do you have any suggestions?