What's causing the stiffness under my chin and sides of my neck?

Lately I've been having stiffness under my chin and sometimes on the sides of my neck. It randomly pops up and will stay for awhile. I try relaxing and stretching my neck but that doesn't help it. Eventually it goes away. I have a misaligned jaw, a crossbite. While its given me jaw pain, I've never experienced this before. What could be causing it?