You have pain in temporo-mandibular joint. Do not eat hard thing, support your lower jaw with your hand while yawning. You can apply warm water wet with cotton over TMJ. You can take analgesic. If pain persist more then one week consult a dentist nearby you.
Jaw joint pain could be due to problem in joint itself or it might be referred pain from teeth (usually from lower last molar). If you have clicking sound, painful jaw movement, face muscle pain etc. Then there is more chance that you have TMJ disorder. Treatment depends on cause and conditions of jaw joint. Consult a dentist who understand and treats Tmj disorder and get one Mouth SPLINT to get some relief. Take hot or cold pack at the joint area (whichever give you relief, take soft foods, avoid grinding and unnecessary touching your opposing teeth, lips should touch but teeth should not in normal time. Take pain killer for temporary pain relief.
You should write about your problem with jaw joint. Usually Tmj disorder causes pain near ear, headache,clicking sound, difficulty in mouth movement, neck - shoulder pain, face muscles pain etc. Treatment depends on the cause and symptoms you are facing with jaw joint.
Visit a dentist every six months for cleaning and a thorough dental check-up. Limit sugary food to avoid tooth decay. Gargle your mouth thoroughly after every meal. Scrub gently to clean your tongue with a tongue cleaner. Floss all your teeth inter dentally & brush twice daily, morning & night, up & down short vertical strokes, with ultra-soft bristles, indicator brush. Tooth brush to be changed every 2 months.