I have had jaw pain/tmj for 4 months now. i eat a mostly soft foods diet, but why, when i turn my heart sharply i get tightness in my cheeks and chin?

See dentist first: Who evaluated your pain? A general dentist, oral surgeon, neurologist or primary care MD? If no consults were done, start with the dentist. Is there a history of trauma to the area? There are many variables to be addressed, see a doctor of your choice ASAP.

See Orofacial Pain: Orofacial Pain provides diagnosis and management of pain in the face (cheeks and chin), mouth (gums, teeth, tongue, etc), temples, TMJ, head, as well as, associated headaches and neck pain. They are the experts in this field.

Dentist: what treatment is planned for that, apart from eating soft food? When you have TMJ, It hurts over the joint, immediately in front of the ear, but pain can also radiate elsewhere. It often causes spasms in the adjacent muscles that are attached to the bones of the skull, face, and jaws. Then pain can be felt at the side of the head (the temple), the cheek, the lower jaw, and the teeth.

TMJ expert: I assume you mean when you turn your HEAD sharply. See a TMJ expert. Any dentist can be a TMJ expert with the proper training and experience. Most commonly, oral surgeons, prosthodontists, and orofacial pain specialists. Ask your MD, your dentist and your dental society for referrals.