Ana positive result (1:1280) in blood tests. All other blood tests normal. What could that mean?

Risk. That may mean you are at higher risk to develop an autoimmune disorders in the future. Since you are suffering from back pain already at your young age, perhaps you should see a rheumatologist to find out if there is any autoimmune disorder affecting your back unless the cause for the back pain is already known.
Pos ANA. Depends on the clinical findings and what other tests were done or not done. May be significant finding in many auto immune disorders. May be false positive or insignificant. It all depends on what is clinically happening with the patient.