My upper left eyelid has been twitching for the past week or so, any possible reasons why even though there might be a wide range of causes?

Myokymia: The most common cause in your age group is myokymia, a benign condition that can be exacerbated by fatigue, stress, and caffeine. It is possible to have a foreign body or other irritant in your eye. It should pass on its own. If not, go see your eye md.

Myokymia: Is a fast twitching of the eyelid. Related to stress, too much caffeine, or lack of sleep. It should resolve on its own. If it lasts more than three months get it checked.