David_166 :
128GB SSD with 20GB remaining
Right.
A couple of things to look into:
hibernation. This will take up space equivalent to your physical RAM.
Disable it, here:
https://www.sevenforums.com/tutorials/819-hibernate-enable-disable.html
System Restore points
See how much space this is sucking up. Adjust as needed.
Pagefile
Depending on how much physical RAM you have, consider turning it down.
I see you have 16GB RAM? Turn the pagefile down to 1GB min/max. You will see zero performance difference.
Games
What games did you install on the SSD? Maybe put those over on the HDD.
Bottom line, though...this is why I stopped recommending 120GB drives a few years ago. Too small, and you run into this situation.
It
can work, but you have to do far more maintenance on it.
240GB or larger these days.