What Causes Nose Muscles Twitching?

the muscles at the bridge of my nose and down the sides of my nose feel as though they are constantly tensed and twitching. It happens all day and night! It started when i was working very hard and under a lot of stress last June - but has never gone away! It also sometimes moves to my lips and you can see them tense and twitch, Any ideas as to what;s causing it would be gratefully received,