My persistent lower back pain had subsided, I believe, because of a stronger musculature around my spine and hips.
I'm sure the 9090 stretch helps but I've been seeing a chiropractor regularly up until getting used to the 16k bell, since I was carrying around my now 3 babies and toddlers about 5 years ago. And I've been using stretching to abate the pain all along. But it was never resolved.
And I haven't missed the chiropractic treatments, as I was worried I would. I have blamed the compulsory carrying of small bowling ball weighted babies for hours at a time, with the development of persistent back pain, and some serious pain developed. I still have one last little one, and I'm not suffering the same effects I saw with the first two.
I guess if I had it to do over again, I might have split up the swings and getups at first, knowing what I know now. Maybe alternating days. And I would have taken longer rest periods at first so that I could be more confident and stable throughout the sets. There was some some instability while I was learning.
I guess overall, my advice to myself would be to play it closer to the vest. Don't force it. The body will adapt as fast as it does. I remember a couple of days it was really tough to climb the stairs. I don't think it was necessary at the time, any more.