I have facial muscle zygomatic in left side assymetry. i didn't have it forever. why, this happens? some days i feel tightness or muscle spasm. i did mri head ok neurology ok oral surgeon ok dermoyology ok?

The premise of your question assumes that you have seen a specialist, in particular a Facial Plastic Surgeon. Isolated weakness of one or both of the paired zygomaticus major and minor (both of which are “smile muscles”) would imply that you have smile asymmetry. Assuming no treatments around the outside part of your eyes with a ‘Botoxin’, the likely causes are trauma or viral. See a Specialist.