Hello mam... Based on your history it seems you may have cavity on your teeth on left jaw....or there may be cracks on your teeth which only cause pain on clenching the teeth....kindly visit dentist for furthur clinical examination then only the correct cause can be ruled out... if there is any cavities then you need to go for filling or root canal depends on extent of cavities....if there is any cracks then crowning of the tooth should be done.......

You have not given any history regarding it means tooth is untreated.  Most common cause for this is your tooth may have deep dental caies involved pulp,  when you give pressor on it it pains because there may be infection below tooth.  Second most common cause is high point on filling.

Namaskaram, Pain on pressure may be caused by a loose filling or a crack-tooth. Cracks vary from superficial ones in the outer layers of the tooth to deep splits in the root affecting the pulp {core of tooth with nerves and blood vessels}. Team Shambhala

good morning mam may be there is some is cavity which on getting pressure experiences pain and then when the pressure is realized the pain go off so you need to see a dentist once for check up You can also practo consult us