There is red spot in my eyeball. i don't know what i did? i was itching it earlier but, i don't know if that caused it. what did i do to my eye?

Likely a bruise: By your history, you likely have a bruise of the white part of your eye, which is actually a thin semitransparent membrane with blood vessels surrounding your eyeball. It's elastic so that while rubbing your eyelids the delicate blood vessels may break and cause a hemorrhage (bruise) which appears bright red. This is usually benign & resolves in 1-2 weeks. Zaditor™ may help reduce itching; tears 2