My experience exactly, although I can't narrow it down to the deadlift. I had occasional but regular low back pain starting in my early-to-mid twenties. There wasn't a consistent relationship with my level of activity or inactivity, the type of exercise I did, or with my weight, all of which fluctuated quite a lot over the years. Back pain was just something I got regularly, like colds or headaches. I've had virtually no back pain (other than muscle soreness and a couple of sports injuries) since I started lifting heavy weights, which is not the usual progression for somebody from their twenties to their forties.
It's incredibly counterintuitive. Everyone's assumption, if they don't lift weights themselves, is that my case is some kind of weird exception or coincidence, and I can't really blame them. I have no idea how to explain that there's a good chance that they are misusing their back, and that they would be more comfortable sitting, standing, walking around, and lying down if they strengthened the muscles in their back. First of all, why in the world would we need to learn how to use our own bodies as adults; don't we figure this out as toddlers? And second of all, if we spend hours every day sitting down, hours every night lying down, and maybe hours every day walking around and jogging, why in the world would our backs not be strong enough to do those things safely and comfortably? Isn't doing something for hours at a time exactly the right signal to prepare your body for doing that thing?
But it seems to be a very common experience for people who try lifting weights: they find that they are much more comfortable sitting at their desk at work and lying down in their bed at home if they lift heavy things on their feet at the gym. I wish I knew how to convince people to try it.