Windows 7 - Partition C(windows partition) loses space very fast - why?

Hi! I know you are probably tired of this complaint, but I really don't know what to do anymore. I already have some folders belonging to some games "dirlinked" in other places; also, the XP MODE files are linked to another partition.
I know you can't tell what exactly is causing my C to get occupied so fast (in the last few days it just got ~1.5GB out of nowhere) - League of Legends installed some updates, windows installed some updates, but srsly, all of those get even 1GB? I know updates make a restore point, and i Deleted them all, I have none of those. I have all useless functions disabled (I know some things about maintenance).
I just wanna know if there is a way to find out what's the last thing modified. I know i can sort the folders and files by "last date modified" but that just doesn't help me.

Today I went with my pc case to a friend's place and I connected the case to his LCD TV. I just don't believe that doing that (the video card adapting to a new display) would occupy my C partition by a few MegaBytes.

So, the question is again: can I find out what exactly are the last changes that decrease the free space?

Examine running processes in task manager - any non standard or suspucious one there ?
There is a free program TreeSize from jam software - examine folders taking most disk space.
Examine C:\Users\<your user name>\AppData
Use CCleaner.

Windirstat is another useful directory size program. It has a nice graphical interface which alows you to ID large files very quickly. WinDirStat - Windows Directory Statistics

Go through each of the steps here and check whether they apply to you.

Hard Disk Space - Free Up and Recover

check shadow copy storage/system protection space being occupied by restore points and the like.
right click computer > properties > system protection
select c: > configure