I'm been taking flexeril (cyclobenzaprine hcl) for years now, and it just doesn't seem to work like it used to. are there any others' that would work better for my back?

Find cause: I think it is remarkable that your physicians have allowed you to go for years treating a symptom without finding and treating the cause of the problem. Perhaps a second opinion with a back expert is warranted after years of ineffective treatment.

None: Muscle relaxants aren't meant to be taken for years (the Flexeril (cyclobenzaprine hcl) insert recommends only 2 - 3 weeks of use). I would argue that for the majority of patients, chronic medications are not a good treatment for chronic back pain. By far the best treatment is to go back to the basics: regular exercise, increased activity, good diet, weight loss, and smoking cessation.