What can cause someone to have a constant off balance feeling, back and pressure in the back teeth, neck pain, headaches and back pain?

TMJ, MPFD disorder. Possibly of bruxing which is a problem of clenching or grinding your teeth. This may cause muscle spasms in the jaw, neck and back. Also this can create pressure in the jaw joint and create pressure on the inner ear, causing pressure, pain, jaw poping etc.
TMJ syndrome. Could be a craniomandibular imbalance. Back tooth pain could be due to clenching. Head posture, neck, shoulder muscles and bite are all related. Vertigo can be related to tm joint compression of pinto's ligament or tension on the eustachian tube. A bad bite can cause these and many other neuromuscular signs and symptoms.
Bite disorders... Bite disorders are a common cause of your symptoms, possibly solved by equilibration (bite balancing and alignment)...
TMJ. All of your complaints are consistent with a TMJ problem. Tmj is a descending structural problem and can cause your posture to change so neck and back pain are a common complaint. Headache pain is usually muscular from unbalenced or poorly supported bite that is not in balance with the body. Higher incidence in females at your age. See a dentist specially trained in TMJ therapy for a consult.
TMJ. TMJ is at part of the problem. Have an evaluation by your MD. Then see a TMJ specialist. Any dentist can be a TMJ expert with the proper training and experience. Most commonly, oral surgeons, prosthodontists, and orofacial pain specialists. Ask your MD, your dentist and your dental society for referrals.