UPDATE!!!!!!!!!!!!!
Well, my injury wasn't nearly as bad as I thought it was. That's the good news. The bad news is that it took me until about ten days ago to figure out the problem.
Turns out, I do not have an SI Joint problem. After I wrote the original post I started researching that ailment. Although I had a few of the symptoms, the people who have that problem are in CONSTANT pain. Me? I wasn't. In fact, as long as I didn't throw any discs, I was about 85% fine. I didn't even need Advil really. But sleeping could be a problem.
So, given that, I was started saying, "It's not an SI problem. It's something else." And I knew it was a spine problem because there was no pain in the discs. It was primarily off to the right side and low.
But here's what I think happened (and a bit of this is guessing because I never went to the doctor's) . . . on the day that I hurt myself playing, I believe--no proof--I believe I tore my gluteus medius muscle. Because days after I wrote the original post I could feel this pain DEEP in the right side of my butt.
In addition, what I discovered is I had a huge muscle knot in my gluteus maximus to the point that the entire lower right side of my back was in spasm. The weird part? I really didn't know it. I didn't figure it out until I really started comparing the lower left side of my back against the lower right side. And I was like, "This ain't right."
Well, my butt and lower back were locked up like that for at least 6 weeks. NO WONDER when I was trying to play that my back lower right side would hurt . . . it was all locked up. But once again, in daily life, I hardly noticed at all.
So, I got the heating pad out. I put it on high and heat soaked that side for like two hours. Then I took a baseball and started rolling it around. Did that for about 5 days straight. And now, everything's great although that area is still a little sore. But as far as I can tell, nothing is damaged.
And that muscle pull that I think I experienced originally is gone. No pain. But I think pulling that muscle caused my pelvis to get all funky. Then the rest of the back muscles and butt muscles on the right side tensed up to compensate. And even though the medius muscle healed, those other muscles never unlocked until I took the baseball to them.
But I went and threw today. No problems. I think I got very very lucky. I really think it could've been way worse. I'm 46 after all. Very fortunate. But now it's like it never happened.