When I get stressed and tired, I tend to get Styes in my eyelids, which are very painful, but easily treated (basically, kind of a clogged folical in your eyelash area). This one was different. It was in the outer corner of my eye but INSIDE my eyelid. I treated it how I normally would for a Stye and .... nothing!
I then put hot water on my face in the shower and it stopped hurting! So I looked up the anatomy of an eye and saw a Tear Gland around that area... so I looked up clogged tear gland and found that it IS possible and does happen on rare occasions. To fix a light case, hot compresses and massaging the gland a few times a day until it is gone will generally work.
I tried it, and have done it twice today, and it feels MUCH better.
Now, I'm NOT a doctor, or a nurse, so I can't offer advice, and I do know that more severe cases may need to be treated by medicine under a doctor's care. But, I thought I'd share this as I'd never heard of it, and maybe my week's worth of needless pain can save you some time and trouble. :)