I have pain in my lower left jaw. it worsens when i stand up and lean forward

Pulled Muscle: The sx's you describe are very consistent with a pulled muscle or bursitis (most likely of the Platysma muscle). This type of injury may also hurt if you open your jaw. If a simple pulled muscle these type of injuries usually respond to conservative measures such as ice, rest (diff area, soft neck brace?), NSAIDS (if able) & improve by themselves. If sev or doesn't get better, should be checked.