I've had severe back pain, right down my spine, for years. Chiro adjustments only provide short term relief. What other treatments should I consider?

See orthopod. I am guessing that you have not had this evaluated by a real doctor. The chiro typically gives deep massage which relieves things briefly but you always go back. An orthopedic specialist can determine the case of the pain and recommend physical therapy, injection treatments and sometimes surgery for more permanent relief.
Prolotherapy and acu. Proloterapy and acupuncture is how we treat our patients with great results.