Ive had that. It can come on if you are stressed or tired, in my case usually the latter - Sty pain is your eyelid and different. How long have you had it? If you are worried or anxious I would pop in and see the doc, no point in taking chances with your eyes. If its something like a sty, they can give you something for it. If its stress related the longer you leave it the worse it will seem - it will only worry you more