What are the symptoms of si joint dysfunction? and what are the causes?

Pain in the very low back (between tailbone and hips) is the main symptom. The main cause is just minor injury -- consider it wear and tear. As people age, osteoarthritis is a common cause, but rarely at your age. Other kinds of arthritis affecting the spine are possible (e.g. psoriatic arthritis, ankylosing spondylitis, reactive arthritis), but SI joint would rarely be the only painful area.

A common cause of SI pain is a limb length difference or pelvic rotation or both. A heel lift with or without an orthotic will level the pelvis and if you over pronate the Orthotic will help. I have this problem and have been treating for over 60 years with success.