Yes, I definitely think some if not all of this is that my core and glutes are weak. I guess I need to find some series of exercises I can do.
And yes, I think a lot of this is related to me doing more cantering now. Part of the issue is that Pony is still a little unbalanced, and he wants me to support his head. The trainer said this isn't ideal, but it's not uncommon in a horse that's still fairly green. It's something we need to work on.
And yes, I know I am not leaning over and picking up things the right way. I guess I'm just getting to the point where I can't get away with that sort of stuff any more.
I'm not sure about the stretching. I do a LOT of stretching, and I've increased it since my back started hurting. I feel like I'm getting a really good stretch in those muscles, but then a couple hours afterwards it seems to hurt even more.
I don't really like taking medicine either, but the Ibuprofen really helped. I am not sure I would have wanted to ride if I hadn't taken it. I'm not going to keep taking it the rest of the day, though. I just took it to get through my lesson. (And even with it, I still made my daughter pick everyone's hooves today.) I also have some ginger oil that I tried topically that helps a little.
I guess my takeaway is that I need to find some core-strengthening exercises to do. And be smart about what I'm doing.