Oradion

try lowering the ram frequency
it sloved a memory leak problem for me at once

You can try to debloat you system and stop processes from starting with windows to help and maybe try something like https://github.com/Sycnex/Windows10Debloater. Make sure you read the page and create a restore point if you use the script. 

If you can add more memory that would be best. windows at idle, depending on background processes,  can easily use 5 GB of ram. my system uses around the same amount of RAM without anything open due to antivirus software etc... It is my opinion in this day and age  to have above 8GB of ram (ideal 16GB cost vs benefit) for a average user that does not do video editing etc.... If you run Arch Linux or something it would be a different story. 

This sounds like a memory leak. Make sure to update all your drivers and uninstall any programs that you do not use. A buggy driver is probably leaking memory and slowly sucking up all of your RAM which is why you don't see it in the Process list in Task Manager as drivers don't show up there. The most common causes are network, (ethernet, Wi-FIi, Bluetooth), audio and USB drivers. Make sure that the latest versions of these and any other drivers are installed.

Moved to Troubleshooting