Windows 7: Physical memory usage increases over time

I have noticed that the problem seems to be something related to sleep. I have 16gb ram and a fresh reboot the system only utilizes about 3.5gb. If I keep it plugged in and running it will hardly ever go over 4gb unless I load up a lot of applications like a VM of which it will then jump to 8gb..... But, when exiting the application it drops back to around 4gb. However, when I close my lid, throw it in my bag and take it to work. After I open it back up I am not up to 5.5, then upon returning home it jumps to 6.5.... then 7, 8 , 9 10... and so on until I have to reboot. Luckily I have 16gb. Could it be that it locks up the ram after going to sleep and never uses it after waking up?