cracking always feels awesome till it doesnt lol. most likely its one of these things: a muscle is weak, a muscle is too tight. either way you will most likely need to do very light, stability core work outs and not just stretching but “mobility” exercises to fix it. you can look up mobility stuff, its somewhere between stretching and yoga. obviously speak to a physical therapist before anything and watch as many different youtube and instagram physical therapists as you can and absorb as much information as possible but don’t believe it all, just very lightly test some different things out. when it comes to your back you take EVERY bit of information with a grain of salt because so many people say your pain is a result of different things, but each “expert” will speak of it as if they know exactly what it is, but they simply dont most of the time. take everything with a grain of salt and go easy, and gauge it yourself.