blurred vision

Hi,

I have always had good eye sight but lately ive noticed my left eye isnt as good as my right and is slightly blurred. its only really noticble when i close my right eye and try reading something but its started to feel a little uncomfortable aswell and when i try to look at something for too long with just my left eye it feels sensetive. Have you any idea what this could be and what i should do?

Thanks