Why won't my eye stop pulsing?

Today my left eye has been pulsing alot and now it’s starting to annoy me. It is now starting to ache a little because of it. I did a google search only to come up with reasons saying it was stress related or that you were nervous about something. I can’t think of any reason why I would be nervous or stressed. Is there any other reasons why my eye won’t stop pulsing?