That's because your back is weirdly sensitive. Ever asked someone to rub your shin? Nope. But back rubs are awesome because your back has a million sensitive spots, all of which feel super fucking awesome when getting tattooed, especially the lower back. You already know that tattoos hurt, and you seem to be acutely aware that the back will hurt, too. You also know that you're already on this path (didn't you just get your hand tattooed?) and that the back is the ultimate canvas. you just need to figure out what you're getting and who's gonna do it, although something tells me that you have more than a few ideas in mind.
While I did find the process to be painful (and expensive), I have no regrets at all about doing it. It was so exciting to see it come together, session by session. There's something about having a full back piece. It's something that I've always admired, but for years, I didn't think I'd be able to make the physical/financial/mental commitment to go through with it myself. Completing it was a big milestone for me, and I have a beautiful souvenir of the experience that I get to wear for life.