Late on in the day your bloodpressure goes up so as you get tired your eyes will start to get a little dryer causing the small blood vessels to break causing a bloodshot eye. To counter this you will need more sleep, try getting more sleep before you have to stay up late and something like an optrex eyemist spray lubricate the eye.
Bloodshot eyes occur when the tiny blood vessels on the surface of the eye become inflamed in response to insufficient amounts of oxygen in the cornea or tissues covering the eyes. Eyes can also appear swollen, watery and tired-looking. Bloodshot eyes can occur in adults and children and are often attributed to poor sleep, allergies or an underlying problem.