Eye randomely gets red?

One of my eyes randomly gets red sometimes. Most of the time it is not itchy, and the eyelid is not even really swollen. I do wake up with a crust over my eye, however. I have had pink eye before and I remember the pink eye being very itchy and downright painful. However, this "random eye redness" is not itchy or painful. It happens about once every month or once every two months.

I am a 19 year old female if that helps at all.