Why am I most unhappy on days when I have neither work or school?

because on those days you are the chooser of how you spend your time and you inevitably choose poorly.
basically you're a born subservient who is unable to direct himself productively.

>>16957632
get a hobby so you have something to look foward to. >>16957812
this basically.

>>16957812
This.

Nothing wrong with it though, you just need to find things to follow.

Some people don't do well "relaxing". They need to be doing something. These people generally function better with a workload spaced evenly across all days rather than cramming work in some days and doing nothing on others.
I'm definitely one of those people. I feel like I need to accomplish something in order for the day to not feel like a waste.

Regardless, you need something to fill your time. Something that is fun and/or productive, preferably both. Keep yourself busy.

OP here. I exercise, make music, play video games and smoke weed. If I get two days off in a row I'm completely bored out of my mind on every single one of these hobbies.