Why is my jaw locking when i wake up?

Possible parafunctio: One reason might be that you are grinding your teeth (or clenching) at night. You need to see a dentist to find out the exact reason for you.

Tmj isk: Your TMJ disk is out of position. You likely have clicking or popping during the day. Likely the popping has gotten louder over time. The locking you experience in the morning is a progression of the disk displacement. The locking will likely become harder to unlock in the morning, You may be progressing to a "closed lock" condition where you can't unlock your joint. See TMJ specialist for options

Dysfunction: Probably clenching and/or grinding @ night. A night guard may help reduce symptoms, but cause of brutish should be found and treated. Malocclusion often implicated.

Classic TMJ Disorder: It sounds like a classic case of TMJ disorder. You can discuss possible causes and treatments of your problem with your dentist or a TMJ specialist.