My jaw clicks sometimes when i open or close my mouth. why is this happening?

Movable disc: There is a disc in the temporomandibular joint (TMJ) that separates the lower jaw from the socket in the skull. If the disc or its ligaments are injured or stretched, the disc can 'pop' out of position during opening or closing. This makes a 'clicking' sound when it occurs. A dentist can evaluate this problem and possibly correct it.

Likey TMJ disorder: It sounds like you are experiencing temporomadibular joint disorder. This disorder can come and go throughout a lifetime or become constant. Signs of tmd are pain in the jaw, ear aches, headaches, popping and clicking, and can cause your jaw to lock. This condition is usually brought on by stress, however can develop overtime if your dental bite is not properly aligned. I suggest a prosthodontist.

TMJ disk out: Having popping/clicking TMJ noises not necessarily a problem. Many people experience these noises. Without pain or limitation of function the noise itself is not an issue. If you have locking or limited movement, "ear" pain, headaches, morning jaw stiffness/soreness, difficulty chewing, bruxism, previous jaw injuries or other jaw conditions, the problem is more serious. Then see a TMJ specialist.