Thank you for your question and for finding EmpowHER. The normal range for Cortisol is 9-52pg/mL, so your results may have been on the low side, but still within range. What do your doctors think you may have? Are you being treated for anything other than the back/neck pain? What is your chronic neck/back pain caused by?
Please understand that we are not doctors and can't tell you what to do or diagnose you. If you feel you want another opinion because you are not getting the level of care you desire, then it is within your rights to see another doctor.
Here is more information about the ACTH test, for you to review: ACTH Test Information, MedlinePlus, and here is information on adrenal gland disorders: Adrenal Gland Disorders, MedlinePlus
Good luck, and let us know how you are doing.