I've been going fucking nuts.

[Atma]

I've been trying to mix ONE song for the better part of three weekends. Like - all fucking day. 

Ears get fried. You start hearing things in a microscope and pretty soon to can't hear the music as a whole. I've started over several times. So incredibly frustrarting.

Maybe you get everything sounding good, except the bass. You alter the bass and then the kick drum gets screwed up. So you work on the kick drum; maybe add more bottom, them the vocals are dead. AHHHH!

Recording the stuff is relatively easy. Mixing is like trying to stack marbles.

Is it your song or someone else's?

If it's yours, maybe the song is asking you to go back to the recording phase and add something. Maybe there's something you wanted to add but dismissed it as more trouble than it's worth, and the song is like "GG... I'm worth it..."

Or... what about sending it to someone who mixes professionally (unless that is you)? Look into people you admire and see who they work with, and reach out to them. After I worked with an engineering genius, it became impossible to go back to mixing (or recording, for that matter) my own stuff (unless it's just for a demo to bring to a studio). 

If none of that works for you, then just know you'll eventually get it right, and when that happens I hope you'll share the results.