Gradual Progressive Physical Memory Usage Increase Until BSOD?

For the last few weeks I have been getting BSOD: IRQL not less or equal, and system service exception. I first updated all drivers/windows ect, and ran recommended repair utilities. After this had no effect, I had been directed by another source to test the RAM, and so ran memtest, finding no errors. I have also swapped out different combinations of my 4 Dimms of RAM to try and isolate the problem. While I have been swapping out my RAM sticks, I happened to notice that my physical memory usage would slowly and steadily rise until ~ 95-99% at which point the BSOD would occur. Since noticing the RAM usage continually rising seemed to cause the crash, I have found that rebooting when the memory usage gets too high will baseline the RAM usage and can prevent the BSOD. Does anyone have any idea what might be causing this? The only programs I'm using are world of warcraft, chrome, and occasionally skype or MS office. BSOD have occured with some or even none of these applications open(But always with memory usage @ ~ 90% or higher). Closing every program when the memory gets high doesn't cause the memory usage to ever stop rising(though it will temporarily drop the usage). So in a nutshell:My memory usage goes from ~20% on fresh boot, gradually increasing until ~95-98% and I Crash. I've scanned the processes>show processes from all users and nothing stands out that seems to be using too much memory.