working Memory set and private bytes related to C# language

Hi guys, right now, I am facing a huge problem. I have designed a c# program but when I ran the program for a period of time (doing the same work over and over all), the working memory (from the task manager) jumped 200% more and it increases slowly (seem to be like memory leak). at the initial period of time, the working set memory does not increase. But when I monitors the performance counter using private bytes, it show a a horizontal straight line ( not linear). But after a certain time, it also increases very slowly. is this memory leak? it seem to be very werid as I thought if there is any memory leak in c# program, one should be able to identify immediately and not after a certain long period of time