Hi Valerie - sorry about your back - it sounds painful! I would recommend seeing a massage therapist first. Your back pain may be from chronic muscle tension, or as you stated, maybe from poor posture. The massage therapist might recommend a chiropractor if they think it might be an alignment issue. That would be my first course of action before seeing a doctor.
To find a reputable therapist in your area check out this website for the American Massage Therapy Association. Look for someone with experience in deep tissue, myofascial release, and injuries instead of someone with a lot spa type experience.
http://www.amtamassage.org/findamassage/locator.htm
I am a massage therapist in Oregon. PM me if you have any questions.
Hope you feel better soon!
--Jennifer