What are possible causes of constant pressure towards the back of my jaw?

Wisdom Teeth. At your age it is not uncommon to have a sensation of pressure in the back part of your jaw. Sometimes just on one side or both sides. I would ask your dentist to take a panoramic xray . Most of us do not have enough room for wisdom teeth and they need to be removed. The earlier the better. Age 16 for a girl is perfect. Usually an oral surgeon or highly trained gp will remove all 4.
Wisdom teeth. Likely wisdom teeth at your age. Also possible TMJ dysfunction if joint pain, joint noises, clench/grinding. See oral & maxillofacial surgeon for diagnosis/treatment.