Please elaborate. Is the pain in the joint (TMJ) or in the actual body of the jaw? Many conditions can cause this problem, including grinding your teeth, clenching, an abscess, an impacted tooth, etc. Can't diagnose correctly over the internet... You need to make an appointment with a local dentist.
Depends. Can be due to any problem in the jaw. Tumor, trauma, TMJ, infection. Bruxism. First stop - oral & maxillofacial surgeon. If tumor, trauma, infection, he will treat if tmj/bruxism, see TMJ expert. 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.
TMJ dysfunction. Temporo-mandibular disorder is the second most frequent cause of orofacial pain after dental pain. Jaw pain, earache, neck pain and headache and are common symptoms. Proper diagnosis is the key to the successful treatment. See an orofacial pain practitioner for a consultation and management of the TMJ.