For the past week my left eye has been twitching frequently every day. what causes twitching? and is it bad that it's so frequent?

Various causes: A muscle twitch is an small local involuntary contraction of muscle. It's usually not a symptom of a serious illness. Sometimes it occurs after muscular exertion.Tension or anxiety can cause twitching. Magnesium deficiency is another cause. For more information see: http://bit.ly/1rBtxRu

Eye Overuse Fatigue: 24 year old male has left eye twitching frequently for one week possibly due to overuse of eye muscle fatigue, bright light, TV, videogame, If no eye Infection or Inflammation, consider too much Caffeine, Alcohol, Smoking, Dust, Not sleeping well, Studying or Reading for long hours and other Stress. Usually self limiting is one rests.

Blepharospasm: This isn't uncommon, and can be associated with many different conditions, notwithstanding stress. In actuality, this is one of the reasons why botulinum toxin (Botox) was approved. While usually self-limiting, this is an approach to take if it is truly bothersome.