Welcome to JA and thanks for asking
The commonest reason for the left jaw pain while chewing is a temporomandibular joint disease. This joint can be effected by various inflammatory arthritis and also some non inflammatory arthritis .A trauma or blow to the joint can also leads to such pain. Till the time you see your doctor anti inflammatory drugs might help in relieving the pain. If you have any other symptom suggestive of any other rheumatic or systemic disorder that too need to be investigated.After examining you physically your doctor can advise further medicines accordingly.
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Now as i mentioned it(TM joint) can have various reasons to be inflamed so first of all your doctor need to look up at it and then advise you treatment accordingly.The time to settle can vary depending upon the exact cause.