Session In oracle

Question

Hi
   I have created service using c# language, it is working properly but problem is there with database session. Session should be created once at the time of log-in, and same session should be maintained till application is not closed or service is not stopped.
But in my case at the time of log-in a session is created, but same session is not maintained through out the process, new sessions are being created, which should not happen.
It should created one session at log-in time, and should use the same session until application is not closed.
What could be the cause that it is creating new session for the same database connection and not using the already created session. 
Event i have closed and disposed the database connection objects carefully.
I dont want sessions to be created. 
Reply ASAP as it slowing down server.
Suggestions and answers are welcome :)