The Problem: my mower deck on my STX38 (yellow deck) is very uneven. I've included pictures below to illustrate the severity, but the deck is so uneven that the right side's guide wheel is actually not touching the ground, and it's (obviously) causing a very uneven mow pattern in my lawn. Also it should be noted that the blade height adjustment bar is also uneven (pictured below). This was actually the first thing I noticed - last time I mowed, I went to raise the height of the deck, and the bar didn't click on both sides together.
What I've tried to so far: I purchased a John Deere leveling gauge, and I've tried performing a basic leveling, by adjusting the three nuts attached around the left, rear wheel well (pictured below). However, this didn't seem to make a dent in the level of the deck at all.
My guess: I'm assuming something is loose at this point, although I can't tell what. I have a manual, but I'm definitely no expert with John Deere mowers, or this kind of thing in general. I'm just a vaguely handy guy (thanks Dad <3). The main reason I think something is loose, is that I can actually press down on the right side of the deck and it seems to spring back up a bit.
Thanks in advance for any help. I've tried to find an answer to this question before posting it, but feel free to point me to another post if this has already been solved.