I'm getting a lot of soreness and cramping in my left hand when I play barre chords, particularly on the acoustic guitar. I've been trying to loosen up, putting just enough pressure on the strings in order to play, and I've also tried to keep my thumb around where my index finger/middle finger is consistently, so that my form doesn't oscillate too much.

In particular, I get these pains while playing "Under the Bridge" by RHCP (in which every chord is a barre chord) and also while holding the chord shapes necessary in "Snow", also by RHCP. I do not think its a matter of strength, because my left hand gets abnormally tired that I cannot finish playing either song.

While playing the electric guitar, this pain is much more manageable (probably because the strings are closer to the fretboard), and I have little to no problems playing individual notes and scales and whatnot.

Any tips or exercises I can do to help loosen up and cease the pain? Thanks.
I know this may sound a bit dull and redundant, But time will cure it.

I got these aches alllllllllll thee tiimmmeee when I was starting, then when I moved on to acoustics.

All I did was massage my hands when they got sore


and after a while your muscles in your hand will get stronger and you wont get sore anymore
It's over simplified, So what!

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^Ish correct, just practice more and eventually your arms will build the strength and endurance.
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Good video (again). Interestingly, I noticed you said that having the thumb pointing straight up is more comfortable. I do have my thumb pointing straight up, all the time, but I do actually find if I point it slightly leftward it sits more nartually and is more comfortable.

Maybe I have a screwy thumb, I don't know, but with it pointed straight upwards, the pad isn't flat to the neck - it kinda faces rightwards.
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