Why am I constantly clinching my jaw? I have to chew gum to keep from doing it & at night my jaws hurt

Stress? People clench their teeth for lots of reason- often stress related. During the day you can put your tongue on the roof of your mouth when you find yourself clenching. Chewing gum can make your jaw hurt more. See your dentist or physician for diagnosis and treatment. Until then, try moist heat on your jaw to try to relax the muscle, soft foods, and anti-inflammatories if you can take them.