Lower Back Question (sorry for the novel)

Hey guys, so I have a question. When I was about 12, I hurt my back while sledding. For several days, my back was incredibly stiff and I couldn't twist or bend over, it was probably the worst pain I've felt in my life. My parents didn't take me to the doctors or any specialist BC they probably thought I was being an exaggerative child; I was a pretty big drama queen. I'm now 17, and I'm having some weird issues with my lower back. I have to pop it a lot. I can feel it going out of alignment, so multiple times throughout the day I have to rotate my hips inward to straighten out my spine and that usually pops it back in place. I can hear the pops. It also hurts when I lay down flat. I can feel the strain on the low back. Sometimes it causes pain down my leg. If I lay for a second and let myself relax, it will pop back into place but I can still feel it's not 100% aligned. My muscles don't really hurt, it's just the spine itself. I also have a very awful and old mattress that probably doesn't help. Does anyone have any ideas on what this could be and if it's related to my sledding injury?