[WIN 7] My hard drive keeps filling up.

I just noticed that my hard drive ( C:/ ) keeps loosing space. My Drive C:/ has a capacity of of about 200 gb. It has about 4 gb free space last week(which is already small I know haha, but I wonder what fills it up that fast) , and I haven't installed softwares or downloaded any files since then. Now I'm loosing space in a much faster rate, just this evening, I have 2GB, but now I have about 200 mb of free space. The Drive D:/ is still fine though. I appreciate any kind of help. Any Ideas? Thanks

[WIN 7] My hard drive keeps filling up.