I have videos of all my lifts here: https://youtu.be/bARmPwL9z-g.

For a couple months now I've been having persistent pain in my left butt cheek (about the place where my tailbone feels like it hits a seat when I'm sitting) that I'm guessing is related to something I'm doing wrong in my squat or deadlift. If it matters, I do not generally have a wallet in my back pockets, and if I do, it is on my right side.

Also, there has been pain in my right deltoid towards the back which seems to be stretched (and to some extent relieved) when I put my fist on my hip and rotate my elbow forward. If it matters, I have been doing weighted chin-ups (I just recently did 3x5 at 45 lb with the last rep being only half completed).

In these videos, I am lifting the following weight (links are to the last set for each):

Squat: 250 lb (link)
Bench: 150 lb (link)
Press: 100 lb (link)
Deadlift: 300 lb (link)

When I first started experiencing the pain, I was up to the following weight for each lift:

Squat: 280 lb
Bench: 170 lb
Press: 110 lb
Deadlift: 335 lb

A few weeks later, due in part to the pain, but also in part to a business trip, I took ~1.5 weeks off to see if it was due to a lack of recovery. However, the pain only decreased slightly over that time. When I came back, I decided to try just lifting the lighter weight to see if that helped anything, but if it has helped at all, it hasn't been much.