I have pain in my mouth. on left side on far back, where jaw connects two parts of upper and lower back teeth. when opnened i don't see anything.

Pain: Pain could be from wisdom teeth, jaw joint dysfunction, infection, and so many other reasons. It's very difficult to see into your own mouth, and self diagnosis without formal training is at best worthless. Please see,an expert, someone who can properly examine you and arrive at a knowledgeable diagnosis.

See your Dentist: You should schedule appointment with your Dentist for Examination and X rays.