I have a white lump like a big grain of rice inger my eye. What could that be?

Pingueculum. The most common cause is a pingueculum, which is elastotic degeneration caused by sun exposure. It could also be a conjunctival cyst. At age 37, it is unlikely to be cancer, but you should go have a specialist look at it. Your eye md will know after looking at your eye with a special slit lamp microscope.
Possibilities. If this lump is on the white part of the eye (conjunctiva) it may be a pingueculum, which is a benign growth usually just to the inside or outside of the colored part of the eye. Lymphectasia is also possible, and this looks like a clear, jelly like substance on the conjunctiva, often near the edge of the lower lid. An eye exam is needed to make the diagnosis.