What do I do about chronic back pain that doctors refuse to take seriously?

Ever since I was 14 (I'm 19 now) I've had horrible pains in my lower back. I don't know of it's nerves or muscles or what but it's a sharp jabbing pain that radiates down my legs to knees and up my back and torso to my chest. I've gone to numerous doctors about it, they've taken x-rays, but can't find what's wrong. Since they can't find what's wrong, they seem to think it's no big deal and I'm just exaggerating the pain. Over the years the pain has grown more intense and frequent and I've grown tolerant to the prescription pain pills they've been giving me, which include Naproxen, Skelaxin, and Hydrocodone. They only gave me Hydrocodone once last year when I went to the emergency room because of the unbearable pain. Since then, however, doctors refuse to give me any "real" pain medications (Vicodin, Oxycontin, Percocet, etc.) because they still have yet to find what's wrong with me. They aren't trying, though, and their idea of figuring it out is just doing x-rays over and over knowing it's going to be the same damn thing it was the first 5 times. They're doing nothing to help cure the pain and refuse to give me pills to ease the pain. It's so bad now that I can hardly sleep at night, I wake up every night writhing in pain, I miss class all the time because hte pain is so intense that any movement cause it to shoot and radiate all over my body, I can't run, work out, play sports, or do anything I used to do anymore, yet the still act like I'm just overreacting. I've seen 4 different doctors about it. They're too stupid to figure out what's wrong so they just assume I'm faking it and trying to get pills. How can I be taken seriously? I've been having to borrow pills from my brother and other friends because of the doctor's reluctance to prescribe me any.