My back constantly hurts all the time. it hurts to sit for too long, to do exercise, everything. went to doc few months ago but it still hurts?

Need evaluation: There are many different causes of chronic back pain. It could be caused by structural imbalances, muscle problems, stress, vit. D deficiency etc. It may be helped by chiropractic or osteopathic treatment, physical therapy, acupuncture etc. If your doc didn't help consider seeing someone else, such as a doc who specializes in physical medicine or osteopath: http://physician.Academyofosteopathy.Org.

Specialist: It is not very common for a teenage woman to have constant back pain. I recommend that you see a spine specialist to diagnose what is the root cause of your pain. You may need imaging studies to help diagnose the pain. Once understood, a treatment plan with modalities such as therapy may be needed.