Application gets slower and slower

My application works under IIS 5.1 and is connected with oracle 9.2
database. After a few days of working it starts to work slower aned
slower. I've checked connections with database if they are closed but
in Enterprise Menager Console - Instance - Sessions all connections
are closed. I've noticed that process aspnet_wp.exe uses more and more
memory, maybe this is the reason? Killing this process results in
getting my application work faster. What should I do to prevent my
application from getting slower. (I want to avoid restarting
aspnet_wp.exe process).What can I check except for connections and
aspnet_wp.exe process. Maybe it's another way to check closed
connections...?