This post is a little out of sequence due to editing.
I find that playing most 7th chords from a root position (with left hand) is a real challenge physically. It feels like I'm contorting my fingers and they get trapped in the keys. I don't know if this a result of me trying to learn this later in life with older hands, or something that is overcome with practice, it feels so unnatural. I would love to hear your experience on this.
Can you post a video of your playing some chords with the Left hand?
Pretty much impossible to comment accurately with such limited information. It is like posting "I don't feel good" and asking for accurate medical advice.
In any case, here are some possible causes of your problem:
* Sitting too close to the keyboard
* Sitting too far to the right or the left so the wrist is twisted while playing chords
* Fingers too thick to fit into the black keys
* Playing too many notes of the chord...the left hand plays in the area of the keyboard where a full chord can sound muddy. Drop a note, (often the 5th) and chords get much easier to play, and are less muddy. (This also can help with thick fingers)
For example, if the music calls for a C7 chord in the left hand, you can play C with the 5th finger, and Bb with the thumb, and fill in other note(s) with the Right hand. And A G7 chord with the left hand sounds good with G played with the 5th finger, and F and G played together with the thumb...a bit unconventional with Classical fingering, but it works well.
BTW, can you find a piano teacher? A good teacher can quickly identify the problem and (possibly) come up with a workable solution. I have had numerous people show up for their first lesson after learning from a bad teacher or from internet videos and/or books, and the cause(s) of the problem they want help with is easily identifiable to a knowledgable onlooker, yet was a mystery to them, and given their abilities, probably not something they could find and fix.