Intermittent eye pain

[TychosNose]

2yo ds keeps crying out in pain and touching his right eye.
It's a bit red and slightly swollen, but that could be from rubbing it when it hurts.

It's been going on all day. He'll be fine for a while then really cry out for a about a minute then it seems to go away.

He seems to be in a lot of pain.

Any ideas what it could be? He doesn't have enough language to describe the pain. Just keeps saying "eye".

Is there an eyelash that's come off and slipped under the bottom eyelid? That can be really irritating but intermittently because if it stays still for a bit it'd stop. Hope it's resolved now.